All units in any X-Com game, except for the invisible and semi-invisible units, are vertical cylinders. The diameter of a cylinder is determined by the LOFTemps used, while its height is determined in the ruleset. It's just as simple.
Thanks for that explanation!
Another thing to keep in mind, is that these only really matter when the game is calculating a "miss" if I understand how it works correctly.
The first thing the game does (after ensuring a clear trajectory) is use aim etc, then random to determine if a shot hits (Center Mass on the target). Any shot that Hits, will Hit, no matter what.
In the case of a miss, it then calculates the trajectory of the miss. This can be pretty broad actually, though I don't know the exact mechanics. Because the miss didn't hit the target, if a unit with Loft Temps 1, was shot at, if the miss erred even on voxel to the left or right, it would miss. If it was loftemps 5, you have a much broader area for a "miss" to still connect with another voxel in the overall target.
How much difference this actually makes, I don't really know.