The measured change in the REFL DC power with and without PRM aligned seems unacceptably small. Something wrong ?
The difference in the power with and without PRM aligned should be more than a factor of 300.
[difference in power] = [single bounce from PRM] / [two times of transmission through PRM ]
= (1-T) / T^2 ~ 310,
where T is the transmissivity of PRM and T = 5.5% is assumed in the calculation.
Also the reflectivity of MICH is assumed to be 1 for simplicity.
We now have (with the PRM misaligned):
REFL11: Power incident = 7.60 mW ; DC out = 0.330 V => efficiency = 0.87 A/W
REFL55: Power incident = 23 mW ; DC out = 0.850 V => efficiency = 0.74 A/W
and with the PRM aligned::
REFL11: DC out = 0.35 V => 8 mW is incident
REFL55: DC out = 0.975 V => 26 mW is incident