Not true.
EVERYTHING on a body is a contributor to final RCS. Literally
EVERYTHING.
The above is an example of how just a small depth on a flat surface can amplify a return radar signal via multiple reflections. That small depth can be a panel gap, which is inevitable on all aircrafts, or a gouge from a tool or someone's boot. The amount of contributorship, meaning the energy level, depends on the radar signal's angle of incident (approach) and the energy level of that signal. Finally, as the aircraft moves and/or maneuver, this contributorship will appear and disappear.
The contributorship, or reflected energy level, of any structure, large or small, can be calculated if measure as a standalone structure, meaning if you want to measure the reflected signal from a screw, you measure only the screw. But the moment you put many many many structures together, measurement calculations gets exponentially complex because reflected signals interferes with each other. The interference falls under two types: destructive and constructive.
Destructive interference is good, basically speaking. This is when signals cancels out each other due to phase/amplitude/freq differences. Between two signals, one maybe completely cancelled out and the other diminished. Or both may completely destroys each other. So for RCS controls, destructive interference is desirable.
Constructive interference is evil, basically speaking. This is when signals amplifies each other due to similarities in phase/amplitude/freq. For RCS controls, constructive interference is not desirable.
When facing a really complex structure like an aircraft, anyone who says so-and-so structure, no matter how large or small, have no relevance in final RCS -- is a liar. Or does not know what he is talking about. If the Americans, and no doubt the Chinese, have strict maintenance procedures on their 'stealth' fighters regarding these small depths on the surfaces of their fighters, then how can anyone say the canards or the IRST sensor bulge do not contribute to final RCS ? These arguments in defense of their nations' fighters contradicts the laws of physics.
