Pretty cool, I got about 10 refusals and no takes. Twice they moved my fly with their nose but did not eat it!!!
Coolness.
If I had to guess, I'd say it was the going underneath that helped. You were on top before, they didn't even notice the thing and kept going like your fly didn't exist. Now you're underneath, and from a distance, it registered as food to the fish.
So one question solved. They are focusing on stuff under the surface, not on it. But something still isn't quite right, hence the refusals. Now, it's probably microdrag, or the fly is sitting wrong, or a color, or 1 size off, or something. Keep experimenting, you're closer now. Just as a warning, you've taken the low hanging fruit on this puzzle, and each step gets progressively tougher.
One thing I've noticed, is that if you can find em rising in a little more current, they're more likely to hit. I'm not saying not to try to finish off the puzzle in slow water. But an alternative thought is to fish faster water. When you're that close, the "exactness" standard is a little lower in faster water. Rises are a lot more difficult to see in a broken surface, though. They're there. You just have to look REALLY close, it's just shadows rising and falling, you may not see the ring on the surface.