Heh - somebody cut off FDR's head and stuck it in a robot.

This is a common with many mecha in movies - there is not enough space in the robot for the human. The Iron Monger from Iron Man had the same problem. Even if there was enough space, the legs and arms of the mecha are too far apart for a human - you would have to rip a man in half length-wise to stuff him inside. Or scrunch him into a ball.

You either have to build Iron Man - a human-sized suit - or a full-sized Gundam. The only intermediate alternative is to use full-blown cyborgs, like in Ghost in the Shell. There most cyborgs have full mechanical bodies, and only meat left is the brain.