For me the fastest vmg upwind on a my chrono is kite low, super powered, kite trimmed (the amount of trim is depended on the amount of power, a race bar set up with lots of trim helps a lot for cranking upwind and setting the correct trim), foil board canted over as much practical. Then dig in and crank hard and fast.
For downwind its finding that sweet spotof max speed/downwind angle. Yes, you tend to be on the cusp of standing up more with less reliance on the kite for stability and hard in cranked not as broad reach which isnt as deep down wind. As you go faster and faster down wind the best angle for max speed changes and the fastest downwind angle actually becomes and arc as the wind window shifts.
To the guys thinking low aspect kite is faster down wind,,,, its not. Sure its easier to go slow going deeper down wind that a high aspect foil. But if you want to go downwind fastest then a high aspect kite will kick the arse of a low aspect kite because it sits closer to the edge of the window still generating power.
The shifting apparent wind window is something many kite surfers haven't considered. The faster you go the further back the wind window shifts relative to you and the kite. The higher the aspect kite you need to keep as fast forward in the window as possible to be able to go further down wind.
After saying all that. I am not a hydrofoil racer. So my advice on actual board technique might not be optimal. I do race kite buggies sporadically. On dead flat hard sand it makes for interesting testing of which kites are fastest. Particularly when you have a guy the same weight as you using a buggy about the same weight, same wheels, same tyre pressure, same dead flat surface, pretty much the same skill level. Then it comes down to who has the best performing kite. We have raced up all sorts of kits from single skin kites to arcs, to leis, to race foils. The most efficient highest aspect kite winds upwind and downwind every time When you are talking hawling arse down wind as fast as possible.
But if you then take those same kites into the sand dunes and race the sand dunes on a course that is undulating and not always cranking the fastest vmg angle and you can now longer go as fast as the wind speed allows and requires a kite that can drift and ride slower and deeper down wind then the low aspect kite comes into play. in that instance the wave kite is awesome.