Slimline set up

What affect does elevation/sea level have on the setup. For instance, if I can get a D* tech to come on his free time and ditter my dish at a spot where it is say 8 ft. above sea level and I take it to a spot where it is 2 ft. above sea level will I still have the same result once I point it at the satellites? I am still having difficulty geting the HD broadcasts when I tailgate.