Now I can sort of answer my own question. I drove way the heck out to Walmart with both kids and picked one up. When I set it down next to my RXT in the car (after assembling it, which took two people) they looked like car seat cousins. They are very similar in size just from looking at them, though I didn't think to take any measurements. Sorry about that. The bottom is indeed narrower than the seat itself and it is a rounded, smooth bowl shaped bottom. That is actually one of the reasons I intend to return it. It would have been for my parent's Mini Cooper which has scoopy leather seats. I couldn't get it in there tight enough and it slid around a lot. Also, the crotch buckle was quite short and it was hard to get my rather small daughter buckled in. The third reason was that once my Dad saw the push on LATCH connectors on the CA we are also thinking of using in their car, he said he vastly preferred those. If he is the one who will be installing and using the seat, I want him to be comfortable with it.
So, aside from the short buckle, the issues I had with it were vehicle/user specific. Overall, I really liked it and am sort of sad to see it go. It feels very solidly built and I like the headwings. Too bad it is so darn ugly. Hopefully there will be some nice cover options soon.