I finished calculating the X Arm loss using first-order perturbation theory. I will post the details of the calculation later.

I calculated loss maps of ITM and ETM (attachments 1,2 respectively). It's a little different than previous calculation because now both mirrors are considered and total cavity loss is calculated. The map is calculated by fixing one mirror and shifting the other one around.

The losin total is pretty much the same as calculated before using a different method. At the center of the mirror, the loss is 21.8ppm which is very close to the value that was calculated. 

Next thing is to try SIS.