Yeah, sorry, there’s not much I can do. Biped is not really possible to “snap” to another rig. It’s all hand aligned, so it “works” but it’s not actually a 1:1 representation.
As long as you do your poses or weapon alignments based on the HeroTPP skeleton and only use Biped to actually affect the pose, then it should actually be ok. Because the skeleton will represent the in game pose, the biped drives it but ultimately the biped positioning may be slightly off. If that makes sense… 
Though what you’re talking about there is a kind of precision that I’d do another way anyway. Using a controller in Max to be able to force the thing dead straight, or whatever.