I think the larger the tilapia, the less likely it'll eat a smaller fish. Of course, that's in an AP system where they are being fed a good quality feed, and enough of it.

We have gambusias and wild Fl mollies at Sahib's. The adult gambusia are probably about 2-3 times larger then the adult mollies.
I'm guessing bcotton's minnows are small like our mollies..?

We have a 75 gallon glass tank with a half dozen adult breeders. There are 2 or 3 mollies in there. They've been in ther for the better part of a year. The tilapia don't seem interested in the mollies.
It is funny when I feed them, the mollies are right up there with the tilapia, trying to get something to eat. If a molly gets eaten, it's most likely an accident... the little guy swam right into a tialpia's mouth...