I had similar issues when I came back to windsurfing not long ago. I had trouble coming to grips with the amount of downhaul required, particularly at spots like Melville where the wind could be quite variable. I was constantly going out with not enough downhaul, but also sometimes too much when the wind was patchy, and having to come in to change it.
I ended up adding a 5:1 fine-tune on the dead end of the downhaul purchase, this gives me a 30:1 purchase and allows me to adjust downhaul on the water, very useful if the conditions change significantly.

The top blocks just have a double loop of spectra above the ferrule that the mast sits on, and this works pretty well. It allows some adjustment of the extension, but obviously if you drop the ferrule on the extension very far you lose travel on the fine-tune.