To Hosakawa:
Sorry but you mistake: the soldiers are managed individualy. So when you merge an upgraded unit with a no upgraded unit, the men of the no upgraded unit will remain no upgraded. The symbol of upgrade is no accurate.

To wingwam:
"...at least be able to split units in half or something so you could mix and match until you got 60."
No you can't. That is a big problem of the game. What i do is: i change the size of unit (to 120 per ex) just before the merging. So i can merge an unit of 30 with an unit of 31 (per ex).