What caused the discontinuity (jog) in the X-bar curve? Would adding another tube at the T running back down to the main hoop to lower rocker tube improve the strength with additional triangulation? Certainly it would add extra weight, but I would be curious how much strength it would add?

Nice work. I'm suprised the T-bar was close to the X-brace, but the impact is in the middle of the tube in the X and at the intersection of the T.