Why not isolate the key motion you're concerned with and examine the basic variables surrounding the "towel pull" or initial butt-cap-first pull out?
Of course you do the unit turn with the off hand high and hitting hand low, in position on the grip as you prefer. When the two hands have taken the racquet around to about hitting shoulder back...you let go and the off arm straightens and swings leftward, the hitting hand continues back somewhat and downward. All this is standard.
The moment comes when you're all set, your stance, the racquet's path, the off arm about to be pulled in, etc. You're ready to launch forward UB rotation. It is at this instant that you will be pulling in the off arm elbow, extending your right leg, rotating your upper body....and...
And? And at that instant you need to roll your hitting arm clockwise as your UB rotates toward the net, taking ESR. This will send your racquet head back and down. The butt cap will be pointing forward and a bit toward the sideline. If you use a conservative grip, the ESR also pulls the wrist in lag. If you use semi-western to western, the upper arm roll/ESR simply reorients the racquet.
I find so many discussions of what happens "to get into the dynamic slot" or in "letting the inertia of the racquet joined to the fast rotation of the UB send the racquet head back and down (relatively) on its own" unrealistic. Just forget the "on its own"rubbish. It is true that eventually you notice no effort taking ESR, getting the butt cap leading way out toward the ball/contact point, but it takes lots of practice, learning to relax, learning to get the UB going fast, learning to love ESR. I think the emphasis should be on achieving the correct arm/wrist positions and the timing in which the upper body leads and the arm/racquet follow "because they must."
Finally, I'll argue this: The main thing you should be observing as you initiate forward UB rotation and the simultaneous rolling of the upper hitting arm back (ESR) is....
This: The crucial instant of your backswing prep lies in how low you take the hitting hand before launching UB rotation, ESR, etc. If you took the hand just a bit lower then take-back-height as you pull forward you are set up to hit quite flat (flat excepting any ISR topspin). If you let the hitting hand descent quite low and back before launch, then you are set up to follow an upward hand-path to the ball, bringing the racquet head under as you pull outward/forward. This low-hand start allows you to generate good topspin both from approach angle and ISR into the hit. In fact, getting the racquet head up to the ball will probably requires ISR as well as approach angle. (Some players think of using strong pronation, not ISR...)
In summary, launching your hit with UB rotation, arm roll into ESR, pulling the racquet forward butt-cap-first...has nothing to do with hitting it long. If you hit it long either you are mismatching your swing speed to an amount of topspin OR you are losing control of the racquet head as you cause it to rise, and therefore are opening the face of the racquet. (or...both).
