I think you slide longest if you sit back in the harness and keep the board more upright. The kite will pull you forwards any way. Kind of like a ballet dancer trying to pop up on there toes type motion. You can also grab the fin under the end of the board which helps slide longer and stalls the kite a little during the loop giving you a little higher pop before landing.
When first learning it also helps to bear down wind when you flip the board over. This will ensure the kite loops and you don’t run out of steam before that happens.
The trick is about 10 years old now ! I stole it off the first person i ever saw do it after having a a session in New Caledonia, not sure it was Tom , some other dude, forgot their name. French people will know.
2009 vid of me doing a darkslide - no idea if i can still do one! probably.. just..
i learnt them just by failing onto my body and keeping the kite in front of me at all times... over and over again...
I taught a lot of people this trick - they can all do it now no problem even if they looked a bit stupid learning it for a while - that is just the way it is - start getting wet...