Ok I'm confused now...is dropout and fade caused by the signal from the sat not getting to the dish, or is it the signal from the dish to the LNB?
The loss caused by rain flowing between the dish and the LNB is so minimal I doubt it can be measured (though snow accumulation on the dish surface can reduce the signal). Rain fade is caused by rain/snow/heavy clouds between the dish and the satellite.
Think of this as a + and - deal. If the satellite sends out a strong signal to begin with, it would take a lot of rain fade loss to reduce the signal far enough to interrupt the data stream. Other things can cause signal loss and they are additive: long cable runs, problematic/lossy cable, poorly installed cable ends, too many splices, a diplexor, a mis-aligned dish, incorrect spacing between the LNB and the dish, poor STB sensitivity, etc. Voom has a poor signal to begin with as compared to their competitors - who seem to do very well with 18" dishes.