I have a dual band beam in my loft space on a standard East West rotator . Can hear and work the Sat's on it but receive is quite poor... what sort of elevation should I erect the antenna..
It depends!
If your antenna can see down to the horizon (where you need max gain) then the answer is 15 deg. See Analysis: http://aprs.org/rotator1.html
But if you cannot hear down there anyway, because you are working through trees and 10 dB of structural wood, tar and asphault (roof) then you should give up on the low elevations and improve your higher angle performance.
But just remember that almost 70% of all satellite access times are BELOW 20 degrees! But if your site cannot see them or work them down there, then give up on horizon gain and plan on having a better signal but only able to work 1/3rd of the pass well.
Bob, WB4APR