OK not to bust your chops, but the way you counted seperation on the KU's is not the same way you counted the KA's seperation.
The 101 is KU and the KA are only 2 degrees apart from it. Based on your KU math. In realality its only 1 orbital location seperatiing them.
So yes I bet the Minimum is 3 Degrees seperation, From KA to KA Which it is 100,101,102
I really don't think there is a formula for KA's next to KU's other then what licences are available for ones orbital locations, and what works without interference at your dish.
Of course Directv wants to be as close to the 101 as then can since thats the heart of of their satellite fleet.
Closer to that means easier to tune.
Lets not forget the Spaceway 1 and 2 (99 /103) first intentions were to be used for internet service. Not tv.