I 'know' many people who have one and even two Regents installed properly in the back of small and medium sized cars
DH drives an Outback Impreza Sport, and the side to side width as well as the front-to-back width are even less than in my Saturn.
I don't get the love affair and defensiveness of the Regent when people point out logistical drawbacks and reasonable alternatives. It's not like anyone says, "The Regent's too big, just get a booster." I bring up the Radian a lot because it's a great, high-quality, easy-to-use seat, with height/weight limits that are more than adequate for average kids to get to a maturity/size to move to a booster.