Just recently I've actually been thinking about how the dome affects the disc, wondering if its just glide. I think it contributes to understability a bit the more dome you have.
I didn't think dome added stability. I think alot of it has to do with the cruising speed of the xcal, being too high for most to reach for long, so the disc appears very overstable. Most overstable discs are flat tops, including the normal xcalibers, firebirds, crushes I can't flip, monsters. This is why I figured some people "tweak" their disc, or push down on the flight plate to flatten their old beat up disc and give it some extra stability. Some models do pull off a dome with overstability though, like the max and the eco xcaliber.
I also recently picked up a 167 champion destroyer for some max D shots, it had a huge dome compared to a star destroyer I have. Found myself getting worked up a lil when I let this guy see it and he started pushing the dome down (out of habit I guess) and started wondering about the xcal and how it maintains its stability.