I don't know much about tuning suspention but how did you tune out over/under stear with the bar? I mean how did you notice and get it right... I'm completely in the dark here. It looks very nice, what lowers are you using?
Stiffen up the rear to get more oversteer, soften up the rear to get understeer. Most adjustable bars you do that through shortening the length of the side arms. That affects the effective stiffness. The shorter the side arms, the stiffer the bar.