Until you have those relationships set, you're working with a servo that will move the throttle more one way than the other.

Having a 90degree angle between the servo arm and the pushrod, and a 90degree angle between the throttle arm and the pushrod is basic. Don't have it and you're wasting time.

Now it's time to see if the servo moves the throttle drum too much or too little. If it moves it too much, move the pushrod connection in one hole on the servo arm or one hole out on the throttle arm. If it doesn't move it enough, move the connection out on the servo arm or in on the throttle arm. When it's close, THEN use the endpoint adjustments on the radio.