When is it time to raise total or bring on another chapter?

[FuzzieAlum]

My alma mater just finished recruitment. Since I was there, the number of chapters has grown to six, and formal rush quota has risen gradually every year from 12-14 in my day to well above 20. I only know this year's results for two chapters - one chapter that always does very well has 28 new members; one that is second smallest has 20. (Four of the chapters are at or around total; of the smaller two, one is local and one is for engineers.) So quota is probably close to 28 - yet ceiling is only 50. Retention is usually very good, too, both during the pledge period and after. Most chapters won't be doing informal rush, of course, and for many girls the engineering sorority is not a possible choice because they aren't engineering majors.

So in a situation like this, is it advisable to add another chapter, or to increase total? I should mention there are three times as many fraternities, but that is partially because the campus is 2/3 male.