I dont do it that way. All deep water here, but I don't edge the board any more than usual. Every foil start begins with the board a bit on edge, but its a pretty smooth drop of the foil as you roll up and over top. I try to edge as little as possible. Thats the secret to efficiency. Staying small and tucked so it takes less pull to get you up and over the board. Its more a feeling of going with the kite as it dives. If you stay legs straight in the water it takes loads more power to get up. Get over the foil with the least resistance and then the kite just has to get you moving forward enough to fly. Do it well and both happen pretty much at the same time, but I think my mast needs almost its full depth to do it safely.
The less wind, the more I need to have the board flat. Really light air starts are excellent basic training for the all in one hole shot up to flying. Its just the same move drawn out with less wiggle room for error. I would imagine the majority of foilers just start getting the all in one start with experience rather than needing to work on it specifically.
If its a beach, I still have to drag out to at least chest depth, and time my hole shot for a piece of swell. Dead onshore is tough no matter what and takes a little extra dragging.
Really low volume boards likely help develop the skill. I do a lot of maneuvering of my foil around in the water with just a touch of line tension and my feet. Have done many straight to flight waterstarts where the board is totally submerged, and I am more or less in a squat but already over top of the foil. Dive the kite and it all goes to forward motion getting you to the surface and flying in one shot. With practice you can do it from a variety of positions. Toe side starts are almost easier to get straight up to flying as your line of travel is typically a bit more downwind.
Now you make me think about it, I did on the Foil Fish, I didn't on the Alien Air (impossible to do basically because of the volume) and I can't remember any other board. My Axis foil is due soon, so we'll see.
Tucked up knees is important too, as you say. Carve the board then it was an almost effortless pop straight up onto the foil.
And I was going to say the same about toe-side starts too
I think there's too much over thinking going on. Have a powered kite and fly it aggressively. Boom, job done.
Now if you want to do it in ultra light wind on a foil kite I have a technique you can try.
Do a back stalled pivot turn on the opposite side of the window, unstall and send the kite straight through the powerzone. It gives you a more punchy power spike to zip you up and out of the water than a downloop.