Hi
It has not been but there are 3 straight sides and the bottom is the only one curved so i believe changing the mounting angle will just mess with the other sides, and if it does improve the bottom it is not likely to make it project a straight edge.
It was mounted a couple of weeks ago by a Promethian Regd installer and has been like that since, it all works and it is not a big curve (5 cm deviation in a 87' board) so all up it is OK but it could be better.
Cheers
Glen