I agree that the OS 70 may be part of the problem. Another club member has a Saito 72 on his and he doesnt have what I consider enough power to be doing any low hovering, his 72 is like my OS 61fx, it has enough power but is marginal when the rudder touches the ground and you have to start staight up from a dead stop, the OS91fx puts you mind at ease cuz you know you have plenty of power to pull out, but without investing in engines I would definitely try some other sizes and pitches, it is amazing the difference when you find the prop that just "works" with youtr setup.