Have a read at the info here
http://www.satelliteforcaravans.co.uk/
A tiny movement of the dish is enough to completely lose the signal. The satellites are located just over 22000mls above the equator, moving a dish say just 1/10 of a degree will move the aiming point several miles at that sort of distance. Best to get a basic lock on the satellites using a beeper then optimise using the receiver quality display. Make tiny movements and give the box time to respond to the movement.
