I have a couple of thoughts. I wasn't sure about the idea that a larger dish would help with the interference problem. The larger dish will collect more signal from both satellites, so you might not be any better off. As long as a dish can collect enough signal from the satellite's footprint, getting a larger dish might only help prevent rain fade because of the higher signal level.

The other thought goes back to my question about the brand of the dish. The symptoms you mentioned, pixellation and lower signal quality, also happened to me with the poor quality Digiwave dishes from 2006. The poor stamping led to a spread out signal at the focus point, which lowered the quality and caused pixellation because of the out of focus signal. It's exactly like taking a picture with a camera where the lens is out of focus, the image would be fuzzy. That same fuzziness can result in lower signal quality and a poorer video image.

The lesson I learned after buying a cheap Digiwave dish was that the difference between a $30 dish and a $50 dish is like night and day. The $50 dish can be aimed in minutes, the $30 dish can take an hour or more because of poor focus. The signal quality from the $50 dish can be very high, the signal quality from a $30 dish was often very marginal. A good 33" dish can be much better than a cheap 39 inch dish.

You'll likely get that dish working but you'll probably need to fiddle with the aim of the dish until you find where the signal is best. I found that a good dish would snap to the highest quality signal in no time because there was only one prime focus point. Finding the focus of a bad dish, because it's diffuse, required a lot of time moving the dish around, trying to find the point of highest signal quality.