This indicates yet another possible solution. Limit the number of
fighting people a noble can effectively lead at one time. A standard
noble could be limited to, say 10-25 people while a combat skill might
allow a noble to lead multiples of that number (twice the number at
apprentice, etc., with experience from combat) and cost 1 NP (since
it effectively "replaces" another leader in combat).
What this means is that when a noble enters combat, his or her top 10
to 25 (pick a number) fighting people will engage if there are more
than the limit. As they die, they will be replaced by other people
until the noble runs out.
This produces a similar result to the "ratio limit" also suggested.
This is just an alternative to adding yet another number to worry