I'm much helped by these leech tell tales. On my boat and sail I now almost exlcusively sail to these WHEN I'M SINGLEHANDING UNIRIGGED. I think this is the result of using a sloop mainsail for unirig use. The lower part of the sail often tends to be to tight for unirig sailing. The top halve is more or less okay as it is cut to twist off more as their is no jib at that height skewing the flow.

We (Blade with Ashby and my own Taipan with redhead sails) are finding that alot of downhaul is fast in very light conditions. We are running the least downhaul in medium conditions then some more in light stuff and even more in really heavy stuff. It seems to help pointing and the sail tends to breath more freely making the boat go faster.

Solo, unirigged in light winds I first trim my downhaul to number 7 (which I can't translate to your settings) then I trim my traveller to have the lowest leech tell tale stream about 50 % of the time; then I add mainsheet till the upper two leech tell tales stream AT LEAST 50 % of time preferable a little more if the winds are unstable. The last seems to allow good breathing of the top. Then a I steer and steer and adjust these settings in the exact same sequence when the wind changes.

I'm finding that like this I do rather well against the two Blades at my club and other boats like F18's and Inter-20's.

I'm finding that oversheeting (top too tight) is really killing boat speed when uni-rigged. It is surprising how much twist you are sometimes using in light airs. The tell tales in my mainsail (not the leech ones) are too insensitive to signal when I'm oversheeting on either the traveller or mainsheet in these conditions.

When doublehanding or singlehanding in more winds then I start using the jib and ordinary mainsail tell tales more but not in light winds. This is for the same reason of insufficient sensitivity.

I have a 4th leech tell tale right on the corner of my squaretop but this one is pretty useless for fine trim. So don't put a leech tell tale all the way on the top of the leach, Have it at least 500 mm down.

Tuning of prebend is an art form in itself. However I do believe your current problems are trim related (sheets, downhaul) and not tuning related (prebend etc)

I hope this helps

Wouter