Suprisingly, I find the Rate commanders gain Star's to be perfect.

(Suprising because I use to think them rediculas)

I guess it has just grown on me, but what I do is send my Consul to fight with half a stack verse whatever I need/want to add to the Republic, he Tends to fight 3/4 stacks-full stacks, and he doesn't gain a Star per battle, but rather after several, I suppose this would represent the fact that just because you won one battle doesn't make you a master strategist, even if it is a heroic victory, It doesnt mean it was because of your general's tactical know-how, The soldier's may have been grizzled, experienced soldiers who knew how to fight and kill, while the enemy could have been fresh leves, farmers, blacksmiths, sheep herders who have no desire or motivation to fight, anyone can make an army of grizzled soldiers beat a group of leves, now of course this is not always true, in some extreme cases, but still.