Hi,
just to clarify, you want just the interior regions exposed? or the outline as well?
unfortunately only signal layers support "rank" so that is likely why your technique is not working with tstop layer
"
Rank
Defines how polygons are subtracted from each other. Polygons with a lower 'rank' appear "first" and thus get subtracted from polygons with a higher 'rank'.
Valid ranks are 1..6. Polygons with the same rank are checked against each other by the Design Rule Check. The rank parameter only has a meaning for polygons in signal layers (1..16) drawn in a board and will be ignored for any other polygons. The default is 1."
But what you could do to work around this is put some ranked polygons on an unused signal layer, then in the CAM processor put that signal layer on the soldermask gerber file instead. (and obviously not on any of the copper layer
files in the gerber).
There might be another solution but im not that familiar with polygon cutouts/rank etc