Look forward to having a locked IFO with ASC signals to further confirm but this has reduced the length to angle coupling by a factor of 5 for X and a factor of 10 for Y (assuming the Len2Ang coupling coefficients in E1200836  are correct!)  This difference is only because the coupling was worse for Y.  The residual with a 200um stroke is now ~0.1urad for both X & Y drive.

See the first attachment for the before picture--this is a repeat from aLog 40106.  That log details the production of the residual Optic motion due to the X & Y stroke shown in the upper right two graph with the black trace being the residual after the length to angle coupling is removed.

Running a couple strokes of sufficient amplitude gave enough info to compute a zero coupling coefficient for the HEPI X & Y to RZ.

The 2nd attachment shows some tests with various IPSALIGN values for Y motion.  There is no oplev len2ang coupling in this DOF.  Final value of -0.0055 reduces the Y to RZ fairly completely.

The 3rd attachment has just the final result using 0.0031 for the X to RZ IPSALIGN value.  The red traces are the X drive and the OpLev outputs.  The blue traces are after the OpLev len2ang coupling removed.  Can't do anything about Pitch but the YAW is pretty much gone.

These values have been accepted into SDF.  Will do ETMY when possible.