basically 2 approaches
I) place mast hand further forward and with a giant tug pull the sail around grabbing with old clew hand to mast end of boom as far back as possible
-- advantage: no sliding your hand forward on the boom during sail flip
-- disadvantage: can't lean sail as far forward and into curve as with front hand close to harness line (and stayig low at the same time)
II) place mast hand close to harness, and -as Egor described- let it slip closer to mast and then tug mast into new direction, sail follows. You can help getting the mast closer to your mast hand with your clew hand tugging/pushing a bit
-- advantage, you can lean sail further into curve (downforce)
-- disadvantage, a little more balance/technique necessary
I used to do I) whith sails up to 9.5 and now am more and more often doing it like II), transistion takes a while but I find it helps with borderline gybes.
the boom-mast-boom method when well preformed (very quick) will not loose much but boom to boom is more efficient (you are quicker out under power and you can stay lower == level and power).