Fundamental/basic rule of tuner configuration is that you must configure based on what is currently connected to the tuner. You are not very clear on what you tests method is. People always post on what they had set before, not what they have connected and set.

Please do the following:
Label the wire that has the motorised dish. Label the wire that has 28.2 only.
Disconnect all cables. Disable all tuners. (I am calling this zero stage)

Test 1.
Put 28.2 cable in top slot.
Set tuner A as simple, single 28.2
Tuner B still disabled

Do you have a problem receiving 28.2?


Test 2.
Zero stage
Put cable in bottom slot
Set tuner B as simple, single 28.2
Tuner A still disabled

Do you have a problem receiving 28.2?