Thank You stranger! I would have assumed the size would vary based on whether your hardware supports the high-quality GPU backend (4 GB) or defaults to a smaller CPU-compatible version (3 GB) but the 22GB note on that page is really confusing. Even if it was including the model server where's the remaining 18GB going towards?
I'd imagine that the 22GB was decided through modelling various scenarios. For a start, it's not just a 4GB current model, it's 2x4GB to be able to update it without needing time when the computer is without a model, that's up to 8GB.
Then it's possible the model you get will scale with the CPU/GPU/RAM available, so if you have a 12GB GPU you probably get a better model, perhaps that's a 10-11GB model? At 2x that's 22GB.
Then consider that a machine is not static, GPUs/hardware come and go, VRAM allocation in integrated graphics changes, etc. You end up with just needing to pick a number and not confuse users.