Broadly speaking, I approve of this idea. The precise details of how large a battle would result in how much honour and prestige would have to be carefully fine-tuned, but raising the honour & prestige gain floor based on the size of the battle is definitely a worthwhile idea.
Maybe instead of making huge battles based on size of units or CS, you should consider it being decided by # of nobles participating in the battle? That way we can also avoid getting notifications about large battles against undeads all the time on Dwilight too
