OOOOKay, before this turns into a big barney, Loco has pointed out that it's a tad difficult to lift a sterndrive by a hole. The anti cav / vent thing is, however similar.
There are two thoughts ref. those plates -
1 - the view loco is expressing - is that to make absolutely sure your prop gets no air from above, you need to run the plate slightly below the water. This will drag more bits of metal through the brine (bad news) but will also give the prop more grip (good news).
2) The view most of the other posters here are expressing - is that once on the plane the water scooting out from behind the hull is coming fast enough to fill the gap where the prop has removed it. Hence, running with the engine higher meaning less metalwork in the water & therefore less spray.
Looking at your pic, I would say moving it down is going to need a chainsaw, so unless you are ventilating with monotonous regularity, I wouldnlt bother dropping it.
Moving it up may cause more ventilation, but I had much the same thing (can't remember if I posted pics or not, but they wrere remarkably similar to yours if I did) I raised by 1 hole & improved the handling, spray & fuel economy. But then I spend a lot of my time moving. & it started to "let go" more often. I cured that by upping the prop diameter by 0.5" (it was well over revving anyway) and so I now have a boat that the prop only lets go if I trim out too far and has awesome hole shot (well, comopared to wehat it was like) If I were setting up a rescue boat that was start - stopping & manoevering a lot then yes, I'd consider dropping it back down.
Horses for courses!
As Pikey says, its a dawdle to raise it, having done exaclty that myself.