Depending on the length of the rod & distance to the bobber ... I usually don't set the hook once I see the bobber go under. I keep reeling until the rod tip starts to bend, THEN set the hook.
And here's the reason :

I don't know which direction the fish is taking the hook, since all I can see is the disappearing bobber .. the fish may be coming right back at me
I'm not really pulling that hard against the hook, but mostly against the bobber, until I get the line fairly straight between the rod tip, bobber, and hook.
That "slack" line (or misdirected line) deadens/softens the hookset. And the greater the distance from rod tip to bobber, and/or bobber to hook, the less hookset power is transmitted to the hook ... resulting in a weak hookset, and less likelihood of hook penetration.

(It's also one of the main reasons I rarely use a bobber when casting)

Have you tried simply casting a Roadrunner along that bank, or even a jig (with plastic body or live bait) ... and just slowly, steadily reeling it back ??

... cp