The walk the talk guys found just the opposite works for longbows. Too strong of a belly caused the glass to shear the wood/glass bond. Unlike wood glass doesn't crysel (sp) so even if glass has a lower compression strength it's not affected like a wood belly. .040 back and .030 belly trapped to the belly produced the best speed. BUT thinner glass on the belly caused the the limb to have less torsional strength so what has worked best is equal glass back and belly