Simple, and somewhat similar to how IR works in game: if your aircraft is heading toward or side on from a radar source, your RCS value decreases, if you turn your back to it, it increases.
I know stealth/ low observable aircraft irl is by far the stealthiest facing the radar head on, and is actually kinda vulnerable pointing its belly or canopy at the radar. Also having sneak mechanics that involve pushing towards an enemy would be novel for a game. But for consistency sake, maybe make it the same as IR where side on is stealthiest, since all AA missiles in game rn are avoided by turning sideways and pressing the "go away" button. Alternatively, make both where head on is stealthiest or leave them as separate mechanics.
I think ive plagued enough posts with this that it warrants its own thread. Also, shout out to any posts mentioning dynamic RCS and having it affect detection/ firing range. Technically it does already but the radars hard cap range always gets hit long before this ever comes into play afaik.