Have you tried calling the quick iso play and then manually calling for the PnR?
EDIT: I assume you are not calling a PnR play from the play menu ( D pad ), and you are just using the button ( L1? ) to call for a PnR manually. I have never had 100% success getting the spacing correct using the "on the fly" PnR. Normally if I call a PnR play the spacing is correct and it works really well.