Hi Ed,
Unless you are targeting suspended schools of fish down deep on your sounder surface fishing is going to be your best bet for targeting Bass on fly in impoundments unless of course you are targeting visible structure .I reguarly fish Borumba and reckon its s great Bass fishery, but Bass are ususaly a by catch for me as I go there for sight fishing Saratoga , lately I have been picking off bass in the shallow sun-warmed bays in less that 2 ft of water with a similar fly , I assume you are using a floating line with a tapered Fluorcarbon leader ( at least 14 foot) for sub surface fishing this will work well, you just have to remember to Slow it down !! even dead drifting when you know that fish are feeding in the area , the only trick as you may know is not to cast at boils because thats where the fish was , alternativly to subsurface my pick for the suface would have to be a version of the Gartside gurgler called the grabhams gurgler its just a lot less bulkier and it creates a more of a waking action instead of a bloop, which I reckon is better for spooky fish and definatly for non spooky fish just make sure you change to mono for your leader as Fluoro sinks.
If you find yourself targeting structure or suspended schooling fish I would suggest changing your line to a fast sink line , I use a SA striper IV it has a sink rate of around 6-8 inches per second ,I tie on this a two peice leader (rod length ) and a #2 Vampire, my go to fly all year round , if I see fish and they are not eating I might try a different colour or sink rate of fly but basicly the same pattern, I hardly change from this because it works. I went out to the local puddle with my mate Tiges on the weekend to christen my expadited #7 GLX and fished the vampire to suspended schools in around 5m of water he was fishing lipless cranks and I was fishing fly and we were pretty much fish for fish it is a very effective way of bass fishing I don't use conventional gear at all , heres a couple with th fly I mentioned