jkilroy,
I'm no expert, but maybe I can help a little. I fish for SMB a lot and do O.K., we got some big ones around here, but I mostly catch the small ones . Anyway, it sounds like you've located them, that's half the battle. If they are following, but not biteing, perhaps they can see you and are getting spooked. If they're nipping, but not inhaling the fly, try what ottaditta said and go smaller, or use a fly with a shorter tail. It works for me. One of the best bits of bass fishing advice I can remember reading was this; think of playing with a cat, teasing him with a string. After a while the cat gets board and will stop chasing and pouncing on it. But let that sucker stay still for a couple of seconds and he'll get all crazy and grab it. Or as he gets closer to it pull it away like prey fleeing their predator and he will chase it and grab it. Same with a bass (sometimes). In fast water I do well to cast across or down stream and swing the fly over likely holes. I like an olive or black krystal flash bugger with an olive over white marabou tail.

Plus I add a bit of red marabou to the head or use red tying thread to give it a wounded look. (Not sure what your bass eat, but try to match the "hatch"). At the end of the swing I will let the fly just sit there in the current like a minnow fighting the current. This is that pause that sometimes drives them nuts and causes them to hit it. Then start to strip it back in short quick motions. If you see a bass come up for it, pull it away like it's trying to get away from him.
Good luck.
Tom.