narf
Sgt. Maj. Buzzkill
I'm not sure if we even have a designation for MCAR. Also they don't always make much sense, my Mustang is classed as a compact despite being almost same size as a WRX
At the very least it should be down in E... I've been looking at US rentals recently for work reasons, C often is quoted as "Focus or similar". I'd be pissed if expecting something shaped like a Focus but got a 500.
As for M, you'd need that if it's possible to rent things like a ForTwo (not saying you should rent one!)... if only to make sure someone renting E (or even C) doesn't get forced into a ForTwo. Might indeed not be a thing in the US though.
As for the Moosetang, it makes some sense to class that as C if in hardtop guise - if you're going by usability, two doors to start with or how many adults you can get in. As a convertible I've rented that under S, and it makes a lot of sense there... but if you book hardtop S you usually don't expect a two-door. The other letters should be used for that, for example the GTI I had in September was CSMR rather than the CCMR of a regular Golf.