Mirror Shift by UFrame

Hey.

MA3100 with an external rotary and a DX100. So let's say I have three parts set up in line on a beam, and these parts are basically snow-shovels with walls, and I'm welding the inside of these walls to the snow shovel lookin' part using coordinated motion, and the profile is ridiiiiiiiiiiculously convoluted so perfecting even just one side took several hours.

Okay, so - parallel shifting the other two iterations of that side? No problem. But when I try to teach a UFrame so as to reflect the weld in the middle on the XZ plane, the result I get basically projects the new weld 90° toward the robot, instead of 180° with a horizontal flip like I want.

If the rotary is positioned -X, +Y from the robot (the program is in RF) does it matter HOW the reflecting Uframe is taught aside from the XZ plane being in the proper place? I haven't had a chance to test much today but I taught my origin->X (XX vector) basically in a straight -Y line relative to the RF, and my XY as basically a straight -X line relative to the RF but the reflecting plane (XZ) should still be smack dab in the middle of the part as a perpendicular wall....

So I'm confused. I'm sure my description has confused anyone who has read it but if you have any insight I'd appreciate it.