Porposing to me is basically thrust amount/angle vs hull speed where the the thrust angle vs speed is at the "hull resonance" for that combination. You can change either and move off the hull resonance point thus terminating the oscillations. The "resonance point" is a smorgasboard of things associated with the boat including hull characteristics, load and load balance, hull to water condition relationship and on and on,.
Raising the engine can get the Anti Vent plate out of the "thrust angle" part of the equation which makes it (thrust) much less predominant. If the leading edge is in the water it acts like a scoop so now you have a scoop and thrust to consider. Jacking the engine up can move the scoop out of the picture and you only have engine thrust which is not as pronounced as the scoop and thrust. I proved this to myself years ago and it's a fact. Before jacking my engine, trim position had significant impact on planing angle of the boat. For a given speed I could set the bow where I wanted it. After raising my engine I got the AV plate out of the water and trim had much less impact on hull angle.
Many times I have been through the resonance while getting up to cruising speed or coming down off it. If I want to stop it at the speed where it occurs and run at that speed for awhile, I have to change the thrust (vector). So a little trim down till it quits and that's that.
So in my estimation you have not reached your resonance point and since you have a variety of thrust and thrust vectors at your disposal (throttle and trim) I'd have to blame it on the boat. Usually that's bad as people ask for help as to how to get it to quit.
Going to say if you have a deep V hull with significant dead rise at the transom it would be much harder to reach resonance that would be the case with a semi V with no dead rise aft.
HTH,
Mark
