Okay thanks! You mean Houdini can bake with different sizes? Also, should I have re-topologized differently to maintain the exact same size, though? I haven't tried Topogun but I'm wondering if something like that would give a better result.
If by size you mean some points are more pushed in/out than they are on the highpoly, that's unavoidable when lowering your geometry count, but the bigger the discrepancy the worse the results will be (see the sticky thread on "Who put waviness in my normal maps?"). However, if you mean by "size" that the model is somehow…
it was said before but again: the highpoly doesn´t need uv´s if it´s used for baking normal maps to a low poly! your main problem here is that your low and high are to different. like BEK said above: small differences in volume don´t matter. you can not avoid this when there is a huge difference in polycount BUT your…