Currently the number of slots for a Planetary Vehicle Hangar are illogical.
Size 2 gives 1 slot with 6/12 mass, size 4 (4x volume) gives 2 slots with 10/20 mass and size 6 (again 4x volume) gives 4 slots with 17/34 mass.
The numbers are more fitting for Size 2, 3 and 4 instead.
Even if someone argues that you somehow need a size 6 slot for 4 SRV it has not even 3 times the mass of size 2 with 16 times the volume.
Size 2 gives 1 slot with 6/12 mass, size 4 (4x volume) gives 2 slots with 10/20 mass and size 6 (again 4x volume) gives 4 slots with 17/34 mass.
The numbers are more fitting for Size 2, 3 and 4 instead.
Even if someone argues that you somehow need a size 6 slot for 4 SRV it has not even 3 times the mass of size 2 with 16 times the volume.