On my end of town, mirror tint is a cop attractor.
No breaks, no excuses, hold your hand out for the ticket.
A "legal" tint is to go side to side from the small marks on the glass edges.
It can be measured horizontally with a level between the marks, instead of following the roof contour.....and that will run it further down the glass in the center.....yet it still goes from mark to mark....
Most shops are in a hurry and follow the roof contour, giving you less tint.-Bob