I don't think the arm length is a problem, if you used a 500 the lnb is off center due to the side by side of two lnb's and also dealing with skew of the dish. The larger reflector should also help as the 129 signal is lower than 61.5 signal. You should use 129 to locate the bird instead of 61.5, even if you find the beam you will not have the change in sound pitch to help you fine tune it and the bar will continuously show 'Wrong Sat' in the bar. If you are working alone makes it nearly impossible to fine tune without consistantly looking at the menu screen. A direct line will also help incase there is some interference from the other lnb's. Make sure you clear the matrix 'Switch Test', before aiming for 129.