It is not unusual for a spot beam to cover multiple DMAs, therefore that TP on the satellite is carrying more than the 4 major channels, maybe 8 or 12 majors plus all the other channels in the DMAs for that spot beam. I'm sure if it were popular enough other channels could be added to PTAT but that would necessitate another watcher for each new channel to mark commercial beginnings and ends - $$$$. When this all began the encoders were not nearly as efficient as they are now, so Dish has been packing more and more HD channels into each available TP on the sats.
I have suggested that Dish rearrange non-network channels on the satellites so that they could also all be recorded en mass, perhaps news channels or sports channels or children's programming, etc. could be recorded with one tuner instead of multiple tuners and the user could choose which ones to watch more easily, perhaps even watch something that was not planned to be watched.