The BIG difference is between the 43dB C/N on the DISH vs. the >56dB C/N on the >3m dishes at the headends et al.
Yeah, your Mods distortion characteristics are great but you still need to identify the "Weakest" link in that chain. Hopefully, there aren't any older launch amps (45dB noise floor) feeding coax out of the building.
How about the return path's QPSK signature? Hmmmmm