Sixt Germany:

BMW 4 series is technically an upgrade from LDAR (don't laugh).
For some obscure reasons, the 4 is LSAR (S for sports coupé), which is valued higher than LDAR. It doesn't fit the needs of some LDAR renters at all (like decent room for 4 people AND their luggage), but it's become popular to give that upgrade.
So you got the BMW 3 series in FDMR / FWMR (Lim or wagon), the 5 series in LDAR / LWAR and the 4 series, which is a 3 coupé with 4 doors sitting in LSAR. You're not the only one to wonder.

For those who think that they would then maybe rent FDMR...
As SUV classifications at Sixt are as bad as for sports coupes, you've got the Tiguan ("SUVed" Golf, more a compact than a fullsize), X1 (SUVed BMW 1 Series) and GLA (SUVed Mercedes A) waiting for you as "upgrades" in FFMR.

Someone really needs to rethink their classifications.