Here are a couple of pics of my car's upper A-arm. There is nothing square about how it's positioned currently. I'm in agreement with you that the geometry gives the car A LOT of negative caster.
Pic #1 is looking toward the rear of the car. Sorry for the poor focus.
Pic#2 is looking down on the upper A-arm.
Does this look like your set up?
I'm gonna have to stare at the geometry a while before I can offer a suggestion on how to get the preferred alignment without all that caster.