And you would be wrong. If that is what you think how RCS calculations work then I hope every Chinese engineers on the J-20 think like you. It would make detecting the J-20 and shooting it down easier.
You are correct -- from reading me no less -- that there are constructive interference in multiple reflections region. But you are wrong in thinking that is how final RCS calculations are derived on a complex body. If the rest of the aircraft do not rise above a certain threshold in measurement, then the inlet regions are irrelevant. Further, the companion to constructive interference is destructive interference so for all you know, the F-22's inlets could produce nothing but destructive interference in relation to the surrounding structures.
Stay out of areas you know nothing about.