You should try it off the grass as well. At least off matts you won't need to clean your clubs! Even so off the grass means GRASS and much of the time the teeing areas at the range can be pretty chewed up and the ground underneath very hard, which is not like a golf course either. The grass should offer a similar lie to a fairway or perhaps short rough. If your trying to hit off of hard-pan it's pretty tough. Also if you're using the tee's not hitting off the grass there's no difference between the grass or the matts -- except you don't need to supply your own tees.