When doing the initial slide to the side and slightly behind Uke, have both hands extended already: the outer hand takes Uke‘s balance and the inner tegatana is on the inside of his elbow. If the inner arm is bent and then tries to extend on the step-behind, it will be pure arm power that does the throw; if that arm is extended and straight from the initial slide, then the whole body is behind the throw on the step-behind.