The charge amplification works on the next STRAIGHT used, regardless of what structure it's used on. Thats a GOOD thing. We call it chambering.
Weirdly, the charge amplification for KICK and UPPERCUT will NOT work on the first held structure that builds the charge, but WILL work on any OTHER structure.
EG. I hold a cube, trigger charge, summon a different cube, i can do a special combo on that second cube with a charged uppercut to start, but not on the original cube, as it would be a regular uppercut.