Not to go on and on about this, but after doing more extensive testing I now have a better idea on how this code works. Testing this code was a little confusing for me and it took a little while to test the limits of it to find out how it works. So for the benefit of anyone testing this code or interested in what all this code does, here's what I learned so far :
The 2-byte value at offset 17012 is your vertical barriers
The 2-byte value at offset 17014 is your horizontal barriers
(the barriers are between the puck and the boards, between the puck and the goal posts, and between the puck and the back of the net)
I've discovered that adjusting the 2-byte value at rom offset 17012 (00xx or FFxx) (the vertical barriers) affects both the barrier of the puck with the side boards and adjusts the location of the side posts of the goal. (anotherwords where the posts are located on the ice, where pucks actually clang off the posts in gameplay independent of the goal / goal-post artwork) If you lower the value of 17012 from the default 0005 to 0001, it will make the side boards wider when pucks hit it but it will also make the side posts of the goal be narrower. (resulting in a smaller goal width)
If you lower 17012 even more to FFFF or FFFD, it makes the side boards even wider, so a bigger ice surface width in relation to the puck but the side posts on the goal become even narrower (so an even smaller goal, a smaller area to score between the two side posts) It seems that if you go lower than FFFD on your vertical barriers you will have to edit the boards artwork and the goal artwork for it to line up. (since the further you decrease this value, the closer and closer the side posts will be to the center of the goal, and the further inward they will be from the side post artwork)
If you increase the value at offset 17012 from the default 0005 to 000D, then the side boards become narrower and the puck will collide "on the ice" about two puck lengths from the yellow line when the puck hits the side boards. At the same time, the goal itself will become much wider and pucks collide with side posts that are well outside the side post artwork. (creating a wider goal and a larger area to score)
So anotherwords you can push the side boards out as far out as you want by lowering 17012 (from 0005 down to 0000, then down to FFFF, then down to FFF0, etc) but it will simultaneously move the location of the two side goal posts further inward making the goal target area smaller. If you lower 17012 beyond like FFFB or something it may become impossible to score goals with the side posts being too close to each other but this needs further testing.
As for your horizontal barriers, adjusting the 2-byte value at rom offset 17014 affects both the barrier of the puck with the boards behind each goal and is the location of the collision of the back net of the goal posts of the goal with the puck. (it may also be the location of the horizontal cross bar) If you lower the value of 17014 from the default 0005 to 0001, this will make the rink deeper behind it goal, the boards behind the goal pushed back (so the puck can travel further behind each goal) and it will also make the location of where pucks hit the back of the goal closer and closer to the goal-line and further and further from the behind-the-goal boards. (get it?)
If you lower this value below FFFF then when you go behind your own goal and take a slap shot it will no longer ricochet off the back of your goal net, instead it'll go right through the back of the goal without hitting it. (and won't trigger an own goal either) FFFF seems to be the lowest value before you lose that back-of-the-net collision so I would stick with FFFF as your horizontal barrier, that's what I'm using now and I think it's an improvement to the default horizontal barriers of 0005. 17014:FFFF makes the behind-the-goal collision tighter, it makes the rink a few pixels deeper behind each goal and it may even affect the position of the horizontal crossbar on the goal. (a win-win, and a huge improvement from default, test it and you'll find out)
If you increase 17014 from the default 0005 to 000D it will make pucks going behind the goal hit an invisible barrier on the ice before it hits the behind-the-goal boards artwork and at the same time will push out the collision of the back of each goal net to be closer to the boards. Anotherwords with 17014:000D you have no room to work the puck behind the goal, whereas with 17014:FFFF you have more room than default and you don't get stuck maneuvering around the back net as much which is a huge improvement. (and pucks still ricochet and bounce off the back of the net)
So for 17014, your horizontal barriers I suggest FFFF. Anything lower than that you will run into problems and anything higher than FFFF (0000, 0001, etc) decreases the depth and space that you have to work behind each goal while staying in line with default board and goal / net artwork.
But for 17012, your vertical barriers, I am still testing values trying to find a sweet spot and to see how wide we can make the rink while still having a functional goal with side posts. Some of the values that produce good collision with default artwork that also give you slightly wider boards with only slightly narrower goal post are : 0001, FFFF, and FFFC. (FFFC has wider side boards and narrower side goal posts compared to 0001, whereas 0001 has wider side boards and narrower side goal posts compared to the default 0005, but you have a little more room to score between the side posts on 0001 than you do with FFFC, get it ?)
So what this code does to the goal dimensions may limit how big we can make the rink while still maintaining a big enough goal, but this needs to be tested further. We are also limited by the player / boards barrier which we don't have a code for yet. However the good news is that right now without making any changes to the art we can use values like [17012:0001, 17014:FFFF] , [17012:FFFF, 17014:FFFF] or [17012:FFFC, 17014:FFFF] and have a slightly wider rink with improved goal / side posts / back of net collision with the puck.
It's a fantastic code here but a confusing one with how it also affects the goal / post / net collision so I had to explain it. Maybe someone with good code tracing skills can see if they can get around some of the limits to making a much bigger rink, but as of now I'm very happy with my smaller goals, better post / net collision with more room to work behind each goal, and with a slightly wider and deeper rink.
I am just thrilled that I found a way to both make the rink slightly wider and improve the goal post collision with just a single 4-byte code which are really two 2-byte codes one for vertical one for horizontal. Honestly pucks warping through goal posts and scoring goals was a big problem I had with NHL 94 on Genesis and this code seems solve that problem by adjusting the goal / net / post barriers as you increase the width of the boards. If you lower offset 17012 your vertical barriers to like FFFD you could edit the goal art at that point to make the side posts a pixel or two narrower but it's still close enough to default artwork. When deciding on a value, it seems to come down to how small of a goal width you can tolerate, how close together you want the side posts to be vs how much wider the rink gets. Oddly enough how the code affects the side goal posts seems to be a limitation to making the rink even wider, but more testing is needed and perhaps through a code trace we can find even more codes that allow us to get around these limits. (I may try hex editing some values near rom offsets 17012 & 17014 and see if I stumble upon any other barrier related codes)
This is a code that truly has improved my NHL 94 Genesis experience, it's amazing how in trying to make the rink bigger I stumbled upon a code that not only did that but also allow us to improve the goal / net / post puck collision issues. If you test out these values I think you'll find that pucks warping through posts and side netting aren't as frustrating when they don't count as goals, because you can always adjust the goal artwork to make the goal smaller, but up until now we had no way to actually adjust the goal dimensions itself independent of the artwork. This is a big breakthrough guys, just in terms of what it does to the goal / post barriers. Finding this code and figuring out how this works is a great motivator for me to continue to chip away at modding NHL 94 on Genesis. I mean with every mod like this that makes the game better and more fun to play it only motivates me more to continue down this road of making improvements to NHL 94 on Genesis.