Unfortunately, that would be bad for my unit diversity since it'd limit me to only 1-2 units of each type.

ie.my army typicall consists of - Greeks: hoplite, light hoplite, elite hoplite, spearmen/hvy spearmen, archer/slingers, cavalry, etc or Romans: trari, principes, hastati, skirmishers, cavalry, mercs, samnites, pedite, etc

If I only had 10 unit slots, I'd either only have 1-2 units each or cut out some of my favorite units. I'd rather have 20 unit types and be outnumbered while still maintaining diversity.