At UCF, according to a recent article / table, and just as a general FYI for people with an interest in UCF:
Looks like all the NPC sororities -- unless I missed something -- are more or less in the same ballpark as far as chapter size (actives and new members/pledges) goes. The NPC sorority chapters appear to be larger than chapters in other councils, in general :
http://knightnews.com/2010/04/frater...izes-released/
For IFC fraternities and fraternities and sororities in other councils, chapter sizes within a given council may (or may not) differ a little more.
For a fairly large school with many sororities and fraternities, there's nothing particularly surprising about the situation, as far as I know.