When comparing run 20437 with IHWP OUT and run 20409 with IHWP IN, with opposite laser helicity for these two runs, the asymmetries of the compton photon scaler channel are:
run 20437: asym = -0.648 +/- 0.032 % run 20409: asym = -0.926 +/- 0.036 %
This indicates that toggling the laser helicity and changing the IHWP state at the same time leaves the sign of the asymmetry unchanged...
Note: these asymmetries are not background subtracted, they are just raw asymmetries straight out of an (incompletely analyzed) ROOT file.