Here's some numbers to support what I am saying. These are AVG readings for an aligned Dish...
119 transponders 14, 15, 16, 21 are all mpeg2 QPSK transponders. 61.5 transponders 10, 29, 31 are all mpeg4 8PSK transponders. 14 is still QPSK. (Are you sure you reported 14 right? And why are you using 10 with only a single unavailable channel on it?) Other than tp14, I see a trend here which is explicable due to the lower signal quality (greater error rate) when Dish uses 8PSK modulation. The FEC is adjusted upward to fix this so that we should get about the same number of dropouts we do with QPSK modulation.
I am not doubting your rain fade experience; I'm just saying I don't theoretically understand it, and I haven't observed it myself. In fact, my experience is the reverse of yours.