I would be concerned that the 225 would be on the verge of being too small on a plane this size with 3D throws, even at 6V. An elevator that size at 45 degrees of throw requires some substantial holding power. It may be too much for the little Hitec mini. If you have zero slop in your linkages and they are not flexing, you have the linkages setup properly mechanically and electronically if using a computer radio, used enough hinges, and the hinge line is sealed, then I would suspect the servos.