High Knob. As others have said, it really doesn't make much difference on a radiused shelf, which has a very small contact point, as opposed to a long flat surface on older recurves. The purpose is to reduce the effects of vertical torquing, which isn't a problem for most folks anyway. Often, however, the strike plate might be built out a little as well. Mostly, that's to tune the bow to the arrow. However, placing the highest point of that buildout over the deepest part of the grip also helps reduce the effects of sideways torque. We're talking very small torquing effects here, probably measurable, but not large enough so most folks would notice them. Most longbows, of course, are straight gripped or have only minor index grips so placing a shelf build up or arrow plate build out over the deepest part of the grip would put them very close to the belly side of the sight window where they would be more prone to being torn or coming loose. Plus, they just don't look very good so off-centered. For what it's worth. Good luck.