I've setup a few with the same problem you are faced with, In hope I can explain how I fix this problem.

I do not know how to change the limits of a retract servo, but here's how I have fixed the problem. I use the small round servo wheel to start with since most retract servos turn a little more than that 180 +/- degrees if I'm correct.

I start with the conection to the servo at say 9&3 o'clock, in line with the retract arm, and if this is not enough move them to to 10 & 4 o'clock and let the connecting rods turn over each other when the servo is cylced. I hope I explained this and I hope it helps.

Flyrcs