No idea what decides the what goes on conus beam, except right now the two sats they are using are not using spotbeams at all. Depending on where you live in the country is what determines what sat you use. Also if you use one that is not in your time zone you will have the wrong time on your sat receiver.
I live in Texas and I use the nearest dma within the same central timezone and I see no difference in time on my receiver. But if "I moved" to say New York I would get everything an hour earlier on my receiver and my time would be off.
The 61.5 sat is stable and has a good signal strength for ,most of the east coast and you can pick it up in the mid west and south. The west coast is where people have problems picking it up. The 129 sat is a wobbly satellite with problems with keeping consistent strength on the receiver. If you get a big enough dish say a 24 "or 30"dish you can get a stronger lock. Also a dish 1000.2 is supposed to get a larger strength on all 3 satellites.
IF you are using simply a dish 1000 for 110/119/129 and no side sat dish to 61.5 then you would only choose a city off of the 129 sat . Presently I am using a dish 1000 for 110/119 and I have a side sat dish plugged into 61.5 instead of 129. Wednesday I am getting the new dish 1000.2 and I will have 4 satellites(110/119/129/61.5) all plugged into one dish. Can't wait to see what strengths I get with this dish. I also should be pretty much future proofed unless Dish adds another new configuration into the mix.
