I bet your bowyer has no empirical evidence as to reason why they recomend the brace height they do. they do it based on myth and speculation or how it's always been.
Well, let me try and help you reason why a brace height is what it is, and why you should listen to an informed bowyer and not a copy cat bowyer.
I hear the hord of bowyers coming.... let me sit back with my popcorn.
by the way these graphs are fairly consistent, they just move about numbers wise. but the trend is always there.