Adjusting the rears so the leg of the UCA is further out would make the camber more positive, not less.
Adjust the front and rears of the UCA’s so that the legs of the UCA’s are pulled all the way in. If that doesn’t get you negative camber then no adjustment on the UCA’s will and you still have an issue somewhere. If that does get you negative camber, then you can cheat the fronts out to get back some more positive caster.
Remember that normally, adjusting the UCA’s so that the front leg is pushed all the way out away from the frame and the rear leg is pulled all the way in toward the frame results in obvious negative camber (and the maximum positive caster). That’s why most people then talk about adjusting the rear leg a little further out, making the camber less negative (but also losing some caster).
Also, when I say to move the leg of the UCA all the way “in” I’m not talking specifically about the position of the adjusting bolt or eccentric, I’m talking about moving the adjuster so the ball joint moves in toward the frame.
