My profile picture shows my Radian installed in the center in my Civic. The Complete Air will not fit because it does not allow bracing. I have my front seats shoved pretty hard against the Radian. In a car where you can't brace, the Radian does, in fact, take up more room than the Complete Air. But if you can push the front seats against the car seat, it allows for a lot more room in the front. In fact, I have the front seats ALL the way back, partly because we're a tall family (I have long legs and DH and the boys are all in the 6 foot range) and partly because with the shape of the seat in my Civic, unless I push it back with the front seats it is over-reclined at 48°.
I am more comfortable now installing the Complete Air more upright. In fact, I did just that in my Suburban yesterday afternoon. The CA doesn't
necessarily perform better in crash tests at 45°. Dorel refuses to come right out and state why they recommend their extreme recline for children of all ages. Now that they have produced a new sticker for some of their seats (the CA included), which will be added to new seats sometime in the future, I think I have a clue. Their sticker states that the seat can be as upright as 30 degrees IF your child is over 22 lbs and sitting unassisted. I think the "problems" they alluded to with installing the seat more upright had to do with the safe transportation of smaller/younger children and not to do with crash test performance.
I am not one to recommend that others go against the manufacturer's instructions, and I still do not plan to recommend that anybody buy the CA for rear-facing until the new stickers make their way into the production line. I am going to try to get Dorel to replace my Complete Air with one that has the new sticker because I actually think my CA is defective. But if you have it, and you can install it more upright to make it fit, I don't think you're compromising the safety of your 3 year old by doing so.