Dowd...
The problem with that is that the radar is based on AGL, rather than actual radar visibility of yourself, and, because this is a world of polygons, there are lots of terrain types where you can be at 15 ft true agl and still be visible on radar. These are usually crucial points which put you on radar long enough for people to know where to look for you, and give them a lot of information about how you are flying.
Upshot of this is that it quickly makes people feel they're wasting their time doing true sneaky flying (used to happen lots in WB in the med terrain trying to sneak in on F2).
So the AGL rates need to be a little forgiving. Perhaps: 50 ft is hidden, 51-100ft gives you away after 5s - so if you're just crossing a funny polygon edge, and you cling to it like momma, you won't instantly appear.
K