I agree from will have little effect with a 9.9hp. My 95 28' Manitou has a 90 Evinrude with power trim/tilt and trim has virtually no effect on ride or speed of my boat. I really only use the trim for shallow water. You must remember that a pontoon is not a planing hull design so you can't raise and lower the bow like a planing hull boat. I would recomend adjusting the trim so the prop is pushing parallel to the surface of the water under power, that should make the most efficient use of your engine.