The wx mode of the S92 radar IS gain adjustable.
Something the size of Blackrock could not be missed whether in WX or GMAP. Quite a large return would be bright red on the screen, whether on a 10mile scale or smaller. Even if the gain was badly set there is still a noticeable difference in return colour. At 200' the tilt would have to be greater than +5 to start shrinking the contact.
LZ