AO bake. gradient at the borders?

hey guys,

i have a problem with AO baking. when i bake a highpoly plane to a low poly plane i got a gradient at the borders which i dont want. tried different settings in the bake ao options but nothing helped. surely i could scale my highpoly mesh a little bit bigger than the low poly. but i hope there is a better way without scaling? maybe in the settings? btw in xnormal i got the same problem.
any ideas?