You can also experiment with this alternative to the circular toss motion... A bent elbow "straight-line tossing motion".
To get a circular tossing motion to result in a straight toss, you have to release the ball early, but not a moment too early. Many players manage to do this well most of the time, but when they get into tense situations, their timing goes off, and their tosses fly unpredictably, with disastrous consequences for their serves.
The solution is to use a tossing motion that may seem somewhat awkward at first, where you start the ball just in front of the leading edge of your right leg (for a right-hander). Instead of swinging the ball out, then up, in a circular path, slant the ball upward and forward on a straight line toward your intended point of contact for the serve. It sometimes helps to imagine that you're guiding the ball up through a pipe that goes to your point of contact. Your arm will look and feel mostly straight during your toss, but you'll naturally bend your elbow slightly in the early part of the tossing motion in order to move the ball in a straight line.
With this straight-line tossing motion, you can release the ball with your tossing arm extended as far upward as you wish, and the ball will not drift behind you. You don't have to worry about exact timing, because with the ball moving on a straight line, it will always be moving in the same direction no matter when you release it.