Even a very shallow one as long as it covers the entire radiator and makes the puller pull air across the entire core. your pusher at idle is only really affecting the area of the fans diameter.
I'm not sure I agree 100% with this. Since the coolant is flowing through the radiator, as long as the majority of the core is exposed to the core opening, I think it's in good shape. If the coolant was static in the radiator and didn't flow, it would be a different scenario, more like what you describe. But say for instance, someone has a 26" radiator where a 22" was......which is a popular swap, cutting the opening in the core support is totally unnecessary, IMO, as there is plenty of core exposed to the opening. If someone has an over heating problem in that particular situation, I believe it will be "somewhere else".
