I do "move" my iron. Not so much lengthwise but more aross the seams, to make them flat and crisp, especially from the front. :mrgreen:
Also, think of the iron as another tool for shaping your block - When my students had trouble getting their blocks to full-size, it was often because they had just dabbed at the fabric with the iron in an attempt to press without moving the iron. They hadn't pressed it out well enough.
Most of the distortion in pieces, especially long pieces, is done during the sewing. You have to let the strips feed through "naturally" rather than pulling on them, but it's hard to do.
Steam can be effectively used for easing in unwanted fullness. I like steam.