Translucent water fine, but submerged objects not so much

I found this excellent video (see attached) describing what’s behind the Water Planes BP available under Learn in Launcher, implemented it and am truly pleased with the realism.
I animated a couple of small fish native to this Texas cave and the translucent water texture at least lets you see the fish, but I see that while the floor of the pool is darker, the depth of the water rendering that realistically, that’s not happening with the fish, which look as bright as if they weren’t submerged. I’ve moved them to different depths and see it’s unchanged. Any thoughts what may be causing that and suggestions for a fix?

Secondly, I with the pawn character could go in the water to see these fish up close, which is possible, but then I see the reflections seen from beneath disappear, bummer. I tried using a second instance upside down just beneath the first, but nada. Any thoughts on that?

Thirdly, not having much luck getting a processing volume working next to this M_Water_Translucent BP. I have it working fine otherwise. Any thoughts on any or all the above are much appreciated.