No that's not normal. Your servo should produce the same amount of torque throughout it's range of motion. Linkage setup can cause an exponential variance at the end of the linkage chain, but the possible cause that springs to mind at the moment, is that if you're using a servo saver, it could be loose/soft towards center and when you set your endpoints out further, you're over-driving the servo saver to the point that it has no further spring action, allowing you to feel the full force of the servo.....does that make any sense to you? Just guessing here.