I know a lot has been said on this already, and all the +1/+2s have been turned down due to having to fit 16 soldiers on that screen eventually, with the potential for a lot of stat increases.
Well, how about we add no extra space? Right now we have one color, green. Stat gains are capped at what, +2 per battle? So all we would need is a yellow +1 and a green +2 in some corner, or stated during a tutorial, and then just colorcode the increases. No size changes, no rearranging...
Information density.