You say that the movement is a certain percentage too much. So you must have measured the degrees of actuation, and then done a calculation.
I would think the the push rods and bell cranks are just a way of getting the movement from the column to the ailerons. What you should be looking for is where are the column stops, and can they be adjusted. On most aircraft the neutral position results in about a 3 degree droop of both ailerons, which goes to zero when subjected to some airflow. The geometry of the bell cranks will give more upward movement than downward movement, to reduce any adverse yaw.