Problems in subtracting 2 segmentations

Hi, all. My case is a cleft lip and palate scan. My goal is to find volume of the bony defect by subtracting the original skull and its mirrored skull. My data looks as below. I know it’s confusing but what matters are just the 2 segmentations I marked yellow: Green (Bone cut) is from the original skull, and Red (Bone cut copy registered) is the mirrored skull.

(If you’re curious with my overall data, the top ones (CTVolume and Segmentation) are the original skull, the Copy ones are the mirror images, and anything below Registration Matrix are the mirror images that have been registered. All transforms are already hardened)

I tried to subtract with Logical Operators and when I click apply, nothing happens. And I want to know what I did wrong. My settings are as follows:

Any help is appreciated!