I'm surprised that the Aceca doesn't look a lot smaller next to the E86 (or rather I am surprise the E86 doesn't look bigger). I've just double checked and the E86 is around 20 cm longer and 20 cm wider than an Aceca.
The E89 is around 15cm longer and 1cm wider than the E86.
The G29 is around 25cm longer and 8cm wider than the E86.
I can buy into the idea that in 2024 the ideal sports car size is bigger than an Aceca... but I really do think at the E86 would, if anything, benefit from being a touch smaller and certainly not larger.
Gotta say the Z4 coupe does a damn impressive job at holding it's own given what it's parked next to.