IMHO....
In this picture
it looks like the motors are reverse trimed. If you take a look at the boot strap, and put a ruler on the picture, it looks like the motors are angled in, underneath the boat. I have been on a couple of boats with yammie 4 strokes that had similar problems, and they required "wedges" to correct the condition. The energy of the prop is pushing up, and pushing the back of the boat up. This is causing cavitation, as the props push the stern up, when you come off a wave, it cavitates, drops back down, and then catches water again.
I think yammie did this on purpose to overcome the additional weight of the 4 strokes, to get the boats on plane faster, so they reverse angle it. Once you get on plane, try trimming up some and see if it helps keep it in the water. The bow should get lighter, and the stern should stay in the water better. I bet this rig is a handfull in a following sea set up like that.
It is really hard to set the height from a picture, but I am pretty sure your motors are too low, not too high. You might want to talk to armstrong, they were helpful when I was setting mine up. BTW, the water comes up about a little over an inch for every 12"'s of setback on the motor.
Put a straight edge on the bottom of the hull extending back, and I would mount the cavitation plates 2.5"'s above that line.