It will help it onto the plane. The cav plate needs to be just under water. Too deep and you will get engine drag and your rig will feel sluggish. Too high and your prop will suck air on turns
The only solution is trial and error as a lot depends on how your rib sits in the water and rides on the plane. Traditional agreed position is 1" above or below the keel line. But with more powerful outboards some are rigged now 2-3" above the keel. This will give better top end speed but you can run a risk of cavitation and you may not suck enough water at high revs in a lumpy sea
If you don't like my opinion, I have others.