I am certainly no expert being new to FTA, but I've seen enough to be suspicious that there are no industry standards in the architecture surrounding receiver design. Even Cisco with all their experience in the industry suffers the same ailments as the cheap Chinese receivers such as the $26 Freesat V7. I'd guess the Cisco D9865H commercial grade receiver incorporates two different and separate processing circuits, one for FTA and another for PowerVU capable of decoding commercial broadcast channels.
Unlike the early days of C-Band, there are no major players in the game like R.L Drake, General Instruments or Scientific Atlanta producing equipment for the FTA market. I would venture to say some of the issues with multi-dish hook ups would still be present if all the receivers in a system such as yours were all of the same manufacturer. I've seen weird anomalies running two receivers of the same manufacturer on a simple dual output LNBF hook-up on a single dish, which would indicate the lack of consistency between supposedly similar components, such as processors and tuning circuits.
I'm sure Titanium and some others in here are far more capable of hashing out your problem than I am. I guess it's why they call FTA a hobby. Even after being in the satellite business for 30 years, I end up scratching my head more often than I'd like when you have a half dozen different receivers, each with its own unique problem. I love playing with this kind of stuff, so I don't get frustrated to the point of pulling my hair out. Hang in there, I'm sure someone in here has the knowledge to find a work through for your problem. Good luck