LF-
V2 is not really a "ground effect" number.
With the advent of turbojet powered aircraft, it was recognized that the certification rules had to be changed. The props had a 50' screen, turbojets have 35'. (And if "wet" today, only 15 feet.)
V2 is really a compromise, not really the best speed for getting off the runway (too fast), or for maximizing the climb gradient after liftoff (too slow).