Barry your speculations align closely with my own.
I have a tentative description which might explain the difference in the two ways of experiencing cessation. (possibly, I'm in no way sure, it's just a suggestion)
There is in the middle of the head a vibratory phenomenon, which could be described as a "strobing", or "fluttering" or "flickering". It is a bit like
this youtube video, but where the tempo is perhaps slightly slower and varies more, i.e. isn't so uniform/constant. To find what I am talking about, you can close your eyes, and look at the center of your forehead, i.e. up and to the center; your eyes will begin shaking at the same rhythm as the phenomenon I am describing. It was made to believe it is particularly evident during the 8th jhana. (in fact this process happens not only in the middle of the head, but that is where it is by far most obvious).
The phenomenology surrounding this process is related to craving / aversion, and all kinds of vibratory phenomena e.g. the breathing wall visual effect is strongly correlated with the rhythm of the strobing phenomenon, in a way that I have come to suspect they have the same underlying cause.
For me, a fruition is something which happens in association with this phenomenon. The strobing stops for a little while, in a very specific special way which I don't know how to describe except that it's a way that I can recognize when fruition happens (this is what I called the "buildup"), and then there is a moment which I would call the moment of cessation, and then the after-effects of cessation.
As far as I can tell, though I could be wrong and missing the full picture, a cessation is precisely a cessation of this strobing phenomenon (though it's not a cessation like you just fixate it or stop it forcefully, it's more like it fades away to nothing), or at least the cessation of something which attention does in relation to this strobing phenomenon (I'm totally not sure here).
If this is correct, then the black cessation / conscious cessation might be simply the result of which side of the strobe is happening when it stops. Indeed the strobe has two sides, a black side and a white side. The black side systematically "covers" the rest of experience, and so I am now speculating that if the strobing stops when you are in the black side, everything appears black, and otherwise not really.
Having had the two kinds of cessation - with black gap, and without black gap - I was generally thinking that when I don't see the black gap, that it was just too quick for me to notice it. But maybe it's something else...?
Sorry for making a contribution with so much speculation and so little certainty, but the above is pretty much along the lines of how I think of cessation, and I am curious if they resonate with what other people are experiencing. Of course it might turn out I am focusing on completely the wrong thing, in relation to this, and please let me know if you think so.