They have engineers that determine bandwidth needs, and no they don't cram too many channels on to a transponder. If you are having pixelation issues you probably have low signal to begin with. With the many different transponders it is possible that your overall signal is low and you're right on the line of cutting in and out and some transponder have just enough signal that you don't see any issues at all then a few transponder even though only a few points lower, are low enough to start pixelating. Whatever channel you're watching games on would just happen to be on a low transponder while the rest of the channels you watch are just enough to not pixelate giving the illusion that it's only on Gane day when oin reality the entire dish needs adjusted.
Could also be a bad connection somewhere. But I would get a tech out to look at it.