Although logical reasoning would be to lower the catch ratings for the defensive players, I'm not so sure that it has any impact on INTs at all. I do have it lowered to "1" in my roster set, just for the sake of trying every possible scenario. But I've done numerous testing with this and the only "for sure" way of lowering the INTs for defense is the slider itself. The catch rating seems to only imply to the offense.
The main edits to help with INTs is to lower QB pass read coverage (yes lower, I dunno why, ha), raise WR run route accordingly if you want (the higher the better, and harder to cover they are), adjust any DB/LB coverage you want (probably lower the LB coverage), and adjust any DB/LB agility you want.
I've been busting my butt to get a nice big type up/article on the ratings (to go along with the next rosters) and how they work over at my site. I'll post it over here as well when I'm done