I agree that transparency is not the perfect choice of words. But that's what I read in a review of the Meostar, the reviewer used that word to describe how the binoculars nearly seemed to disappear when held in front of the eyes.
I believe you agree that the physical shape of the binoculars has an impact on how much of the visual field they obscure.
As I have tried to show, my hands must be in the equation because at least the right hand intrudes. It has to be right there in real use.
Admittedly, some binoculars permit a better grip like you described, but I doubt that could be done with the stubby Zeiss. Although slightly harder to quantify, it should be mentioned for binoculars like these that the hand may obscure the visual field to some degree. For others, that would be needless and thus easier to assess how the binocular itself promotes or obstructs the PFOV experience.