I disagree that a plane should be trimmed at full power unless you are planning to race it... Let me explain this: If you fly at full throttle throughout the flight then by all means trim it at full bore... If you mostly fly at 1/2 or 3/4 like a aerobatic plane then trim it between 1/2 and 3/4 throttle... Full scale planes from a cessna all the way up to a jetliner constantly retrim their plane for climbing after a take off, cruising, descent, approach... Changes in weather i/e temp, density can change your trim setting for level flight from day to day or region to region... For a model it is a little but of a pain in the butt to retrim throughout the flight so find a trim setting that is close for all power settings and you will need only a click or 2 on any given flight... As I stated before:

"Any airplane will climb with throttle increase and the opposite with throttle decrease... Trim your airplane at the mean speed you plan to fly... "

If you find that your plane climbs tremendously then you may have a thrust line problem... Roll inverted and see what happens... A thrust line problem can be fixed at the field with some washers under certain bolts between the engine mount and the firewall...