Strategy for foiling downwind

Its all about line tension, rather than trying to point down wind.
The more tention in a reach you have the the more you accerlate. If you point downind it reduces tention and you slow down.
So focus on finding a balance, between building tension & getting pulled/pointing downwind... focuss should be on line tention not how deep you pointing.
Since depending on kite size & kite type & wind speed & your speed you doing wil sll vary how deep you able to point at a given time.

Good way to practise is start a reach,... go for a good distance feel the tention build in the lines and then slowly let it start pulling you down wind... you'll start to speed up, your throttle now becomes pointing deeper (reducing tension) to slow down or speeding up by pointing less deep and increasing line tention.

Exactly what PKR said ! Riding powered downwind is all about keeping tension in the kite lines and generating apparent wind. Ironically the faster you go downwind, the more apparent wind you create and the more "upwind" you are riding. The top guys look as if they are in the exact same stance down and well as upwind edging hard against the kite. Think about Nico parlier doing 41 knots downwind in rockingham lately, he's riding at twice the wind speed and is effectively kiting upwind in relation to his apparent.

Im not good enough to ride my race foil kites like this, but I feel I am ok with my much lower aspect lei's. With no trim on and sheeting in hard, you can work your way deeper letting the acceleration keep building until you chicken out and stand up. When the line tension falls away and the kite begins stalling, pointing back up a few degrees is usually enough to reset everything and you can then point back down.