Kudos on your creativity! I doubt that I would ever have come up with a setup like this - I really like how you regularly push the boundaries with growing (Cephs, Utrics, Heli's, etc).
I would have thought that this was far too wet but the results say something different. I've been keeping my original mother plant (on a moss-covered cork slab) drier than last year & it looks like I'm losing some of the 'expansion-outposts' it had established. I need to turn this trend around - the other plants that have been kept wetter are doing much better - including the jamesoniana (where the bottom 0.5-1 cm is often submerged).
I have two distinct colonies of U. campbelliana on the sponge, one at the bottom, which is in the first pictures, and one higher up. The one at the bottom is much wetter and the plant grows much better there. Indeed it has put out a new leaf right on the waterline.
My personal opinion, and I'm sure many will disagree, is that perhaps we try to emulate the natural conditions too much without taking all variables into consideration. We know the 'typical' humidity and temperatues on the Tepui and can emulate them, but they are just a small part of the vast number of variables that environment will be subjected to. This brings into question whether the variables that we can control are influenced by other variables in the natural environment that we don't control in cultivation, i.e. can one without the other actually be detrimental or of little benefit?
Any updates on this?? Looks very very interesting