I made a quick texture-based explanation.
To answer the main part of your question, the tori/uke head is mostly spherical. while it's not perfectly smooth, it IS round and not an oval in any way (99% sure).
however, the way the texture mapping is done causes massive amounts of distortion at the top and bottom of the texture ingame, the top and bottom quarter or so of a texture are compressed immensely.
here is a quick, ugly texture i threw together. it's just a thick line going vertically through the face and all the way round. Ignore the bend in the center, and compare the top of the head below with the top and bottom of the flat, hopefully you can get an idea of how much is pressed into that top bit.
and the flat