Google Rhop it's well documented.
Essentially an extended concave contact patch.
Applies a lot of hop with very low pressure, centres the BB extremely well.
The SixG Nub will hop most weights of BB, but again it is very good at centering the BB.
Heavy BB weight is desirable in gas guns due to joule creep, which allows extended flat flight, which is also less affected by wind etc.
Yes smaller the barrel higher the pressure, however it is best to have the BB float on a 360 degree cushion of air, without going into it deeply, 6.03 best compromise power (distance) and accuracy in MWS, 6.05 best accuracy.
Id only use 6.01 in a pistol, and it needs to be kept cleaner than usual.