You can't even compare the Blvd to the AOE.
We are using my sil's AOE in dh's car right now, rearfacing. I offered to trade her for our Fisher Price Safe Voyage Deluxe, not b/c I want the AOE, but b/c my nephew had outgrown his AOE, and he has to stay harnessed--he's only 26 mos old (and huge)! We also have a Britax Decathlon and an older Evenflo Triumph Deluxe (not the new higher weight one).
I HATE the AOE! (Did I mention that I hate the AOE?) It adjusts easily (harness can be moved into a new position from the front), the harness tightens and loosens super easily, and it's fairly deep, so it's good for ds to stretch his legs while rearfacing. But aside from that it's a huge PITA! It is nearly impossible to install properly rearfacing. You can't get your hand thru the belt path at all, and the cover does not open up to give you access to it. You have to unhook the cover (difficult as well, esp when installed or trying to be installed) to reach the belt path, and then, once you've actually got it installed, you'll want to hook the cover back...but you can't without breaking your wrist and screwing up your installation! It also sits so low on the seat, that most seatbelt's female end get hung up on it somewhere, making it likely that you'll think it's tightly installed only to find out later that the carseat has slipped totally or the belt comes unbuckled.
Yes, I hate it!
Get the Blvd if you are comparing. It will fit in the center just as likely as the AOE, and it won't interfere with the seatbelts. It will install easily, as all Britax convertibles do. If you prefer to spend less, get the MA.
If you need to spend less and still want a great seat, get the Evenflo Triumph Advance. It's wide, but you may still be able to get a great center install, and even if you can't, I'd rather my kid be in it outboard than that stupid AOE anywhere! It has EPS foam in it as well, and the AO's do not (well, maybe one or two "top of the line" models do, but only in the headrest! HA!)
The ETA, MA, and BLVD will all last your kiddo rearfacing a year or more longer than the AOE, and they will definitely last longer overall. They have taller top harness slots and taller shells than the AOE. Most kids who use the AOE outgrow the harness when they could still be harnessed in one of those other seats, and it makes an iffy booster. If a child is that small/young and going into a booster, it's the last booster I'd want them in.
Another option that's narrow and may install well in the center is the Sunshine Kids Radian 65. You can do another search on that on the boards.
hths
henrietta