From my tests, \galley_cutout_*:nn calls don't interact well with 
\galley_margins_set_*:nn or \galley_parshape_set_*:nnnN

Indeed, cutouts seem to completely ignore any margin or parshape and 
compute the cutout from the full galley width. Is that expected ? (I 
cannot find any mention of that fact in the l3galley documentation)
Of course I understand that l3galley is an experimental work in progress.

I might try to write a patch if the current behaviour is to be changed, 
but I am currently buried under heaps of exams to grade so don't expect 
anything soon.

Cheers,

Julien "_FrnchFrgg_" Rivaud