Before lining up the optical links, you have to take care that the input signals do not exceed the maximum levels (see Specifications on last page of this document)!
In the standard configuration you should have approx. 4dB gain over the whole optical link. Due to variance of laser- and receive-diodes you might have some gain-spreading between different links.
When connecting an occasional use antenna, point your dish to the satellite with the highest total power. This is to ensure not to generate a maximum level fault during normal operation.