For OTT the projectile travels OVER the forks which means it doesn't need as much of a fork gap as TTF where the projectile (as well as the pouch) travels through and in between the forks. You can imagine then that a wider gap might be necessary to facilitate that. However, narrow fork gaps for TTF exist as well though they are suited for more seasoned TTF shooters. And yes, there is an issue of fork hits for someone not used to shooting TTF. An example of a narrower regular production frame would be an Axiom Champ. And there is also a video somewhere of someone shooting TTF through a 1 inch fork gap... So, small gap TTF shooting is possible though it may not be for everyone... For OTT you can actually shoot without any gap - pickle fork style - though a specific technique is necessary to ensure the projectile lobs over the frame.
For fork gaps and widths, I think it comes down to personal preference (be it OTT or TTF). As we learn to shoot and get acustomed to an anchor and reference point that works for a given fork width, I think we'll tend to favour that width. IMO it doesn't make any difference for accuracy as it is just preference. I won't say that a particular width is intrinsically more accurate than another. It really depends on the shooter, it always does.
We shoot best when a frame is within the parameters of our preferences. Having said that, we can all shoot different frames... just takes a few more shots to dial into accuracy but I believe we'd still prefer to shoot more relaxed with our preferred frame.
Hope this helps!