[PGSigns]

Here is why the bag behind the axle will ride the best. With the bag on the bar you loose leverage to lift the truck and the closer the bag gets to the frame mount and the more air it takes to lift the bag to a set point. So with it behind the axle it may take 40 psi to keep the bag at say 6" and the truck at ride height and with it half way down the bar it will take about twice the amount of air to keep the bag at the same height. A bag with more air pressure will be stiffer. a stiffer bag is a stiffer ride. Goal is to have the bag at ride height about the same height it is sitting on the bench with no air in it.
Jimmy