Could you baseline the product by taking a shot of just the neck - the empty section, however small that is - as a sort of ‘tare’ like on a scale? Then, presumably, you’d have an accurate basis, no?
all rights reserved on special ‘tare’ aspect of forthcoming premox collar
That works if the fill level is low enough - but many wines in burgundy-style bottles (in good condition) have fills that go underneath the capsule - so no way of getting a good read on the color of glass.
The bottom of the bottle would be tough to get into a gap with a small circumference. Maybe a horseshoe or as “C” shape rather than a collar? Or if the collar is locked in as a design decision, perhaps a flatter disk, like a thick washer, with the active components sitting raised on opposite sides of the disk?
With different bottles composed of glass with different absorption spectra, I’m not so sure that even this part would be easy if there wasn’t enough headspace in the neck for the gadget to take a reading through the glass alone.