Weed fins for most of the popular Australian shallow, weedy, speedy venues are generally short in depth but still large in area.
12cm Tribal Delta weed worked perfectly for me at Lake Budgiewoi in my CA40 with 5.2m sail for 39 knots.

Mast Track as far back as I can get it.
Many weed fins move the centre of resistance further back. When I change from an upright fin to a 40-45 degree weedy, I have to move my mast track back to stop the sail foot dragging in the water.

When using a 50 degree and more, wedge shape, or "Delta' shape, there is usually quite a bit of fin in front of the box so the balance is more normal, but they don't 'lift' the boards as much, so mast track back is still usually the way to go.