The grooves act like vents to take away dust, heat and gasses which build up on the pad surface.
Thus if the grooves are spinning so they touch bottom to top of pad, the dust/heat/gas is expelled out.
If the grooves touch top to bottom of the pad they are expelled in towards the centre with no where really to go.
Thats how I understand it.
HOWEVER I do know some top brands of aftermarket grooved discs have instructions to fit them as Ozone has.
Thus if the grooves are spinning so they touch bottom to top of pad, the dust/heat/gas is expelled out.
If the grooves touch top to bottom of the pad they are expelled in towards the centre with no where really to go.
Thats how I understand it.
HOWEVER I do know some top brands of aftermarket grooved discs have instructions to fit them as Ozone has.
Wishes for more power...