Best configuration so far is 

bko:1 when background substracted
ko:0 as it is quite stable over a PS1 image

the number of stamps seem to be quite important setting nsx,y=10 works better on most image (less over substraction) but crashes lamentably on some others part of the image.
Setting nsx,y=20 avoid the crash but at the cost of more oversubstraction in the other part of the image.

Regarding the kernel, setting auto works relatively well.

sigma PS1 varies from 0.62 to 0.69

sigma FRAM varies from 1.77 to 2.33

kernel match varies from 1.65 to 2.24

Does not affect much the result, default returns correct results

Change to 3 polynoms of order 2 seem to be better. 


For one case need to set nsx,y from 10 to 20

For another cas need to set last sigma of the kernel from 3 (if default) to 5
