Sorry Brad, I've only made 2 glass bows from scratch. My intuition about core thickness would be to have the lower limb be relatively less thick, or less stiff, less positive tiller. But honestly I'd personally take this small adjustment with sanding over using stack height. Best I can figure, the limb you get out is a crap shoot at best, within the tolerance of stiffness you'd need for tiller, given a particular set of lam stacks and glue up cycle. Best to fall back to the tried and true method, figure the stiffer limb out once they are made and adjust if necessary.
I'd adjust the effective lenght with the riser, rather than the limb itself, by placement of the fulcrum and arrow pass.