im not sure about the peavy but fenders usually have a 10-42 dia. flat wound strings are harder to bend because the core is more rigid than round wound strings (flat wound have hex shaped cores i believe and rounds have a round core).

the fender fingers easier because the butt against the fret with less pressure than rounds. height and width of the frets might also be the difference here to.

thats the best answer i can give but the experts here might have something that makes a little more sense.