I believe they put a seal around the radiator support so that the only air entering is from the grille. The grille does not keep the finer particles from going through the radiator.
The problem I am having when mowing with my 4720, is that the finer dust/grass particles are clogging the condenser causing the a/c stop cooling. This is frustrating in 100 degree heat! I have to blow out the intercooler, oil cooler, condenser, and the radiator out every 2-3 hours. When I blow them out, I can't be sure I'm not bending the fins with the air or nozzle because of the spacing between them.
I have addressed this issue with the dealer and they assure me that it has been reported to John Deere. In the meantime, they tried to adapt the earlier plastic screen to my tractor with no success. Hopefully they will figure out how to line the inside of the grille with a finer screen.
If anyone else is having this problem, I would encourage them to report it to John Deere directly or through the dealer. Without enough case files, they probably wouldn't be too motivated to correct this problem.