If the reflective surface of the new dish is smaller than the current AT9, that may make rain fade during heavy rain worse than it is now. With a smaller reflective surface less signal will be reflected less to the LNBs. We might be better off with the AT9 if it's reflective surface is larger.
Rain fade is a big problem for us here in Florida, during our heavy summer showers.
Actually, we haven't experience that yet this year with all the dry weather, but when it starts we will have to get used to the daily signal loss during the showers. Good thing they only last a few minutes.