I have estimated how the mode profile of the PRM reflection should be, as shown in the plot blow.
A conclusion here is :
we should be able to constrain the PRM curvature situation if measurements are precise and accurate enough with a level of less than ~ 100 um
In the calculation two cases are considered :
(1) PRM has the correct curvature of +122 m. This is shown as solid curves in the plot.
(2) PRM has a wrong curvature of - 122 m (mirror is flipped) This is shown as dashed curves in the plot.
I have omitted the effect from the PRM thickness. Therefore PRM is dealt as just a curved reflector with RoC of +/- 122 m in the calculation.