Gravity is a force too, just as much as the force from an engine, or sail.( what about water skiing? The force undoubtedly comes from an engine, but the water skier planes from the force of being pulled by a rope, balanced by the planing lift of the ski - no prop lift there) the point is, the surfboard planes without 'lift from the prop'.
I suppose you are saying the 'manufactured' boat you have does not plane? you say the thrust is VERY negative; does this imply the craft does not perform? because you also said that any negative angle will keep the boat from planing. which is it? you seem to have contradictied yourself, or passed it off as an exception; while I see two examples of 'manufactured boats' with negative AOA. this would seem to support that the 'manufactured boats' do it for a reason. One would assume that a manufacturer would do some research to give a modicum of performance, if nothing else to retain customers who are satisfied with the performance of the boat, rather than produce a dog of a craft that will give the company a bad name.