I'd imagine you can do just about any size you want. It's amazing how much more effective cooling is with 2 fewer layers between the die and cooler.
I recall a much older thread where another G12 user had a 120mm AIO on a 2080Ti. I thought there was no way that would work. They proved me wrong.
There's also my own experience, but I didn't go that small - I tried out both Celsius S36 and Celsius+ S28 on my 1080Ti.
If you want any chance of mounting the radiator to the rear or the top of the chassis, you'll need an Asetek-made AIO that uses angle barbs from the pump head. Mounting the Celsius S36 up top wasn't possible, but the Celsius+ S28 worked because of this.
The 360mm could be front mounted, but I noticed that it wasn't any...