Yeah, I'm with you, I don't care either. I actually like the coverage concept of Sirius. Because the system is designed to tolerate satellites moving, they can add more into the system, if they wanted. Like two more sets of waltzing birds, one over the east coast, one over the west. And they'll do a better job of urban areas, if one of the satellites is high in the sky, in your location. (Which is why XM needs terrestrial repeaters in urban areas.)
Trees? At that frequency? Not much you can do but wait until the fall...
I agree, gain is not a problem when the satellite is in sight, but the free space path loss from a Sirius satellite might be less, when it's overhead. I haven't checked in to how high either one's orbit is, or the ERP of either. I might be interesting, just to see, as that would help determine how much foliage either one could tolerate.
Of course, if you're in a position to see at least two satellites at once, this could help. (Depending on receiver design.)
Neither service discloses much about their technology, however. Even the suppliers of test equipment for them, are very tight with detailed information. Rohde & Schwarz, for example, can emulate the satellite constellations for XM and Sirius, in a lab, so that receiver designs can be tested. Or if one satellite is good enough, they can do that cheaper.
It's very high level, but there's some insight into the structure. They talk about Sirius being two satellites. Effectively, that's true, because one of them is always in the southern hemisphere.
http://www.rohde-schwarz.com/WWW/Publicat.nsf/article/n175_smiq03s/$file/n175_smiq03s.pdf
Woa, we sure did dive deep into the systems, but the first step in truly understanding dropouts, is to understand the system's tolerance to poor signal conditions and how they get created.
Remember, the dropout you hear, occured about a second before you hear it. So the off ramp, may be the result of going under a bridge, just before it.