Fancy aspect ratio talk aside, all you did was resize the screen to 640x480, which well fair enough, you can scale it however you want, I just never implemented it because it's an 8bpp game so any kind of decimal resize will not be smoothed and probably look like ass, but if some people like it, I'll throw it in at some point.
And I'm not sure X-Com was designed for 4:3 anyways since the PSX version is 640x480 and it just letterboxes the 640x400 graphics.