A little head tilt helps if done just as the final traps squeeze is needed. No, you don't have to think about straightening it until the ball is gone.
The point of the head tilt (or, for Edberg, the head tilt/turn-back) is just to mechanically assist/help trigger... your flex of your trapezius muscles. For their role in the backhand watch some good OHBH slow motion video filmed from behind the player, linked below. If your torso balance is slightly forward at the start (or at least not leaning back), which it will be, then the slight head tilt just as your hitting upper arm passes even with your leading foot.....should leave you feeling your traps coming into action...and pulling your shoulders back will launch your hitting arm forward, up, and rightward. Add a little ESR (If that's not familiar, ask) into contact to boost topspin.
If you turn your grip a bit more around to eastern backhand+, you'll have more options, such as increased sidespin, a more diagonal lift into contact.
The head tilt won't be of much use, though, if you aren't aware of the "pull your shoulders back" move in the first place. To get the importance of the thing, just do this: Stand somewhere with a racquet in your hand, BH grip, upper hitting arm at your side, forearm extended forward, racquet pointing as much leftward as your grip provides just before you'd be pivoting hard into the ball. Now, rotate the racquet/forearm to your right just using shoulder and back muscles but NOT moving your hitting upper arm from your side. That's the acceleration you can add to your swing, as those muscles are faster in action that your trunk rotators. Add a small amount of ESR directly into contact both for power and to keep the racquet face slightly closed.
Back to the Head Tilt: The traps (the top band of the three-band muscle) flexes to hold your head up, its key function. If you're slightly torso forward and tilt your head forward loosely, you'll feel the traps automatically "catch" your head...and you just run with that, generalizing it to the middle band (main...) traps. As you get the thing, a full trap squeeze becomes normal, controlled as needed. This "squeeze" retracts your shoulder blades as described above....but, relevant to the OHBH, causes your shoulders to rotate backwards (and down a bit), causes your hitting arm to move rightward and up toward the incoming ball. This is a fairly fast and powerful action. As a bonus, the non-hitting arm also gets rotated back and upward. You don't have to think about it much.
As to the relative position of the hitting shoulder back and just into forward launch, the head tilt, the traps flex (shoulders flexing back), watch the video slow mo hits ten times. Figure it out from what you've read. At about 3:04 in the slow mo some backhands appear. In the non-slow mo version of that same video (the second link) you can see what that OHBH sequence looks like at full speed beginning at: 1:30. Use the space-bar or screen-click and the , and . keys to go frame by frame on either video
There's not much more to know that can't be seen. Look (on the full TS backhands, not the light fast pop BH's) at his back and shoulders. Look again. Try it out. The thing flows directly from the initial rotation to the (somewhat optional head tilt &) and traps squeeze. If the traps are unfamiliar, Wikipedia does a decent article on them.
