Hi Alexey,
Yes I've optimized the alignment, first by just the GPS camera position (from a Cessna 172) and then after I accurately placed all 67GCP's I've reoptimized it again with all the camera positions unchecked and just the GCP's. In the ground control settings I've set the marker accuracy at 0 since they're measured with RTK GPS.
Photoscan gives an error of 0.036m and 0.768 pixel error, does this sound correct to you?
PS, I'm on the latest version and build.