Mad Old Lu
Super Freak
It's likely HT would use the same exact body. I don't think Cap got smaller in the movie. But I agree with you, he needs to have good range of motion for posing, but should NOT look any smaller than the First Avenger figure.
Any suit that tight is bound to restrict articulation as well.
The TT advanced has just about the same kind of muscle shape and mass, but has the usual double jointed elbow and complex shoulder/chest joints. Since it's all hidden under the outfit, they can totally use that body instead of the sculpted muscle body. That muscle body was completely unnecessary on the First Avengers figure. Some people even swapped out the bodies on their FA Cap and you can't tell a difference at all in the overall shape, but they have much improved articulation.