There is no possible way to increase it above 20.
MaxPhysicsVehicles is now limited to a maximum value of 20. Your server cannot handle more than this. If you think it can you are wrong. If you complain about this I will ban you.
This is why.
Wacky. I'm sure I've seen servers with more before that was put into effect...
My dogfight had about 30. I loaded it the day v13 came out and thought rtb prefs broke. Then when I saw the change log i got really pissed off knowing that fort wars servers will suck due to not being able to have vehicles because the limit was hit.