Excellent pix. Puzzle finally solved! I see that BMR makes a massive poly bushing for the axle end of the UCA. BUT BMR also read me the riot act, and said NOT to use it, if a BMR poly bushing, like used in either version of their adjustable UCA, is used at the front of their UCA.
IE: Don't use a 'poly to poly' combo on any UCA. BMR (Kelly, when he was still there) told me to instead either use either the oem rubber bushing, OR use the STEEDA spherical bushing. He said that 'Poly to Poly' would bind up in the corners. The BMR axle end poly bushing is only ok, if a spherical busing is used at the front end. Spherical to spherical would be the ultimate for handling...... but will also result in terrible NVH.
I have the original (05-10) version of the BMR UCA....and oem rubber bushing at axle end. If I had to replace the oem rear rubber bushing, I would use the 11+ BMR UCA...and the steeda spherical rear bushing....then call it a day.