I don't know if there is any real secret.
I'm just short of 6 ft with longish legs.
I have a Corbin seat which is very tall, which actually makes knee down more difficult not easier.
I have Renthal ULs which are very low and forward in comparison to stock bars.
I easily hook my outside knee under the flare out of tank by ankling my foot.
I hang from that, outside butt barely on inboard of seat area.
Well off to the inside and down.
Yes, knee should touch down before anything starts dragging, although that statement is much more so if one has stiffer springing than late model 919s.
04 and later are so soft, they really compress down once loaded up in a turn.
Also, if your right foot peg was not folding, I doubt your brake lever hit first.
Was the peg folding while you had your foot on it?
Anyway, most unfortunate, but at least you got off not bad, aside from your ground off knuckle.
A good way to figure out all this body position stuff is to try it in your garage or on your driveway.
Get a race stand.
Get a stool that is similar to the height of the foot pegs.
Wear your leathers and boots.
Hook the right knee on the tank, and use the bars.
Now manipulate your left leg such that the sole of your boot is against the side plate above the peg.
Just doing this will force your knee out and down.
Next get your butt over to the inside, and start working towards getting the knee down low.
You may find to really get down, you'll have to have your inside forearm hanging vertically below the grip.
Depending on the stool or chair, you may be able to get the kneed down such that it's resting on it.
If not, you'll appreciate having it there should the bike start to tip when you're trying all of this.
Find a position that works, and it will feel strange and have to be "learned".
"Learn" the position at rest, not at pace!
Do the same for the other side.
Then learn how to move from one to the other.
Then learn how to speed that transition up.
The next time you go to the track, it will feel familiar and then you can start refining things based on your particulars.
Plus, you'll never have a trapped foot squished by a heavily loaded folded peg.
This is all 70s era Superbike racing stuff, so if you want some guiding and inspirational pictures, you know what to look for.
For the lean angles and peg heights of a tracked 919, the old school way is great.
Not good for serious super sports at pace though, as their lean angles are so extreme there simply isn't room to do King Kenny Roberts knee out style.