Prefacing a bit, if your Soundwave's thighs stick out in tape-deck mode, then the inner hip joints and thighs are mismatched. Undo the five screw on the back of the figure's pelvis and the three in either thigh to put them back the right way around, and that is how MP-13 was "intended" to be assembled. However. That misassembly put the thighs closer together in robot mode, which massively improved Soundwave's proportions. Using a bit of spatial reasoning I figured out that swapping the knees/thigh assemblies around entirely allows for the better proportions while still keeping the bottom of the alt-mode tidy. As an added bonus, since the joint now sits on the inside of the thigh in robot mode the silhouette of the legs is cleaner too. This can't actually be new, right? I googled around briefly but I couldn't find anything about it being done before.