You just need to remember that a TTB suspension is basically two levers that pivot at one end with the wheel at the other end. Both the bumpstop and shock are at mid-points on the lever... If the lever (axle beam) is able to move up say, 3" where it hits the bumpstop, the wheel (at the end of the beam) can move up maybe 5". So it's definitely possible there's 5" of uptravel, and 7" of down, for a total of 12" at the wheel.
And I hope that it's just the angle of the pic and I'm not seeing a gusset up at the top, but that tubular radius arm with the upper tube that appears to be welded straight to the side of the axle beam right in the middle is a failure waiting to happen. The radius arm needs to span the entire width of the axle beam top-to-bottom (including the section of box tubing, if used) where it attaches to the beam.
The driver side radius arm alone bears the entire torque load being generated by the front differential, so it needs to be sturdy as possible (and gusset up top or not, the tubes should be gusseted or plated along sides for support also). For those here building their own arms, take a look at aftermarket arms such as Skyjacker or Camburg to get some ideas.
I'd also suggest try to design it so that it's similar to the OEM coil spring setup where the radius arm bolts to the axle beam rather than having the arm welded directly to it. To me it seems this way it would be even less likely to have a weld fail in this area over time.
