When the mirror is placed on the printer, I have about 1 degree of movement on each side of the the axis before it bumps into the 'legs' with felt pads that support the mirror.
I understand that you may not want the mirror touching the pads all the time, but I have noticed that when I have a print on draft quality that is near the edge and quickly moving back and forth (perhaps infilling in a small cross-sectional area) that the mirror jumps and wiggles all over which must impact the print quality and accuracy.
I've not had a chance to try on a finer setting.
Should the mirror have this much tilt? Do I need to adjust my legs up to help better support the mirror?
So on my printer, the interference fit with the center bearing on the y-axis carriage is very snug - I found that I had to push fairly firmly on the build plate to seat the mirror, not just set it down. With this done, no wobble and much better prints!
Beginner mistake that is easy to make if you are in the habit of breaking things when you push on them!