Yeah, I'm not sure what you're talking about either. Maybe this will help... maybe not.
When I make a bamboo backed trilam, I make the center lam and the belly lam approximately the same thickness at the bow's center. The bamboo backing is tapered. The middle lam is tapered, and the belly lam is parallel. The degree of taper of the middle lam is determined depending on how I want the limbs to work.
The belly lam is left parallel to allow a little more wood in thickness for some tillering or weight adjustment without rasping or sanding down into the glue line, but... BIG BUT here... the key to realizing some of the real benefits with these bows is to get your lam thicknesses and tapering accurate enough and close enough to final dimensions prior to glue up, that minimal weight and tiller adjustments need done later. Not unlike with glass and wood laminated bows, precision and record keeping are helpful.
The way I do it, the backing, middle lam, and belly lam are glued up in one shot. When it comes off the press/jig/caul, the handle piece is shaped to match the profile and then it's glued on.
The belly lam should be a wood that is great in compression resistance. If you want to play with different woods like cherry, walnut, sassafras, yew or whatever for the center lam, that's fine, but it's hard to beat osage or ipe for the belly. Although, boo/yew/yew or boo/yew/osage are great combos too. Lots of options.
