Problem Solved - Thanks!
With the help of a trusted adviser, we identified the skin rivet issue to one of the dimple not being deep enough. Someone suggested that earlier in the thread and they were in fact correct. (thanks for the feedback!) I use the DRDT-2 instead of a C-frame, and getting the right amount of preload , as it turns out, is quite important. I hadn't been squeezing the material hard enough to allow the spring back dies to do their magic, thus leaving a quarter sized region of deformation in the skin vice the very localized yielding of the metal in the immediate location of the hole itself. In all clad parts like the skin, widespread distortion is also evident if you look at your reflection (as if you were looking into a mirror) Despite a witness ring on my first attempt, a correct dimple manifests as a series of concentric rings indicating full engagement of the dies, so now I know what to look for.
I opted to drill out any fasteners already set to remove the HS skins and send them back through the dimpler and the new results are superior. A few hours lost but thankfully no parts harmed.
RV-7: Working on Empennage