I actually only had one pad in the hammock earlier in the week, so the stacked pads might have had something to do with the discomfort. When I stacked the pads, I ended up only partly overlapping them, so they were wider at the shoulder section, which is where I was having the most problems staying on the pad. I did have a heck of a time keeping the pads underneath me, and it seems like it would be even harder to get good coverage with only one pad. I might have to try the "wings" idea of something like an SPE to try to get some coverage for my arms with a single-layer pad.
I still think I had the hang screwed up somehow - I tried the hammock out after I took out the pads while I was tearing down, and I still had that weird "feet higher than my head" feeling. I was making sure to keep my feet in the footbox but it didn't seem to help much. I think I've just got to experiment with it some more.
I really need to get me a hammock stand so I can try this stuff indoors without scaring the neighbors at night setting things up with a headlamp.