When I raised the back of my Axiom with OME 912 springs I encountered the same issue, the traction bar hitting the gas tank and not letting the rear axle drop all the way down. I guess a bent or rewelded bar that would clear the tank would definitely let the rear axle have more articulation.

02 Axiom, 2.5" Indy4x Lift, Rancho 9000sx, 265/70 17 ATs, awesome Shrock Works sliders, flipped ball joints and a PV muffler.