Sorry guys I would have to respectfully disagree here. As with a bow that is say an ELB style, which is signifacantly short of center....form is going to affect your arrow flight more then on a center shot recurve. Obviously stating that we have taken the time to find the right arrows for the bow which we know to be the most important part of our game.
Think of it this way. A bow that is at rest with the center of the shaft centered through the bow. With a good form, you're going to have little to no torque, good release, no movement. Which means your arrow is horizontally affected less as there is no bow to wrap around or deflect off of due to human error alone from shot to shot. It's one of the reasons people can and regularly do shoot recurves well making a host of errors be it form and or spine or a combination of both.
All things being equal, having the proper spine out of a non center shot longbow, the farther it is off center the more those horizontal errors are going to affect it. Its simple physics...the more bend the arrow has to go through, and the more bend the arrow is put into, the more inconsistent your arrow flight and over all accuracy is going to be. The less the arrow has to work around the bow, even with a greater then normal horizontal screw up will show less down range inconsistencies. The best we can hope for is to do it the same way every time though that eludes many of us at some point through our careers as traditional bowhunters or primitive bowhunters.
This can go one step farther, as it was noted a long time ago. I happened to find this in "the bowmans handbook" (and no it's not for sale). The chapter is on "design and construction fo an arrow vibration frequency meter. The jist of it? Like spined shafts bending disemilarly. This is taking things to a level we need not go to....yet to say it doesnt affect accuracy? YOu can see similar concepts and theorys state by most of our greats in the past. Yet very few take it to this level.
As for the shelf itself.
I'd rather have to build a plate out, then have no shelf as on my old Doug Knight excaliber. IT does shoot well, actually extremely well. And when I screw it up, it screws up extremely well too
. Yet it has very very little there for a shelf and for the longest time was a problem with getting feathers gouging into the bowhand and fine tuning that bow. There is no reason a bow that requires a shelf measurement cannot be cut past and built back out to achieve it. Why go through the trouble? I've greatly noticed a difference probably from my lack of form and shooting flaws without the pressure points as I do with them. Both Asbell and Feguson go into discussiong this in both there books. As does some older perodicals referencing Fred Bear. If you're good enough you probably dont need it.....atleast for me I do!
There is a reason many of us present and those of our past spend so much time practicing form!!! There is a reason Howard could shoot many different spined shafts out of his bow and still achieve great success down range.... Flawless form, he knew as many do and have, it's importance.