In the past weeks, I did the following two measurements;

1. Polygon disabled
Vibrations caused by the rotating fan moved the laser spot in the order of 50 micrometers.
With a disabled fan the laser spot moves in the order of 4 microns.  

2. Polygon Enabled

I adapted the firmware so I can use only one facet. The laser spot moves at maximum 25 microns over 30 measurements. The exposure strength varies a bit on a facet-per-facet basis. The spot is slightly distorted due to the scanning; 37 micrometers x 77 micrometers. The spot size also varies  per facet; some spots measured ; 34 x 110 micrometers.