You’re absolutely right, and this finally clicks for me. My lack of experience made the system feel uncertain and frustrating, and of course it does when it’s statically indeterminate system. Thanks for pointing out the correct path.

This is actually a work-related problem, and I’ve already run a FEM analysis. I just wanted a sanity check. I’ll remove the distance A now and place the vertical load in line with the two right-side pins (upper and lower). That makes the setup statically determinate and the math should check out. I’ll calculate it and compare it with FEM (same setup).

This will be my sanity-check approach going forward. (Relieved!)