I have more of an ATP forehand in that while tacking the racket back it always stays on the right side. The coach described it as quite whippy.
He now wants me to move towards a loopier takeback with a laid back wrist during the whole motion.
From your description, it is entirely possible that you don't have an accurate idea of what the essentials of a so-called ATP-style forehand are. It seems to me likely that you, like many players, don't examine a variety of ATP forehands to see what they have in common. The videos, and in super slo-mo, are widely (and often freely) available.
Two commenters suggested going to an Agassi-style forehand. His was in no way significantly different than a contemporary male pro forehand: I have a few of them open on my screen at the moment. What makes his swing look shorter or more compact is just this -he keeps a bent hitting elbow all the way through the stroke. If Agassi straightened his hitting arm during the swing down just before first forward motion of his hitting hand, his arm would be arranged (in terms of angle back and racquet face closure) much the same as Fed's or others (Nadal).
Agassi did include the keys to a contemporary forehand, as far as I'm concerned: he did a full unit turn 90º+; he took the racquet back with his wrist extended ca. 45º back, somewhat less than Fed et al, but not much; his last upper arm motion before lowering was to pull it back into tension; he used his off-side arm much as Fed et al do, extending it to the side high, then swinging it downward and left to give it momentum that he'll use at launch by pulling the elbow in, shorting the lever arm, which sends rotational momentum to the torso just when needed (he'll flip his off-side forearm up just going to contact, slowing torso rotation extremely briefly to send mo to the forearm).; Most importantly, perhaps, he launches the forward motion via upper torso rotation, which is critical to quickly accelerating the heavy upper hitting arm; just as he starts rotation he rolls the upper arm clockwise in the sholder socket, aka ESR (and yes, until it becomes second nature you do that intentionally).; exactly into contact he rolls his arm counterclockwise into contact, ISR.
If those are the things you do, then you're doing an ATP-style forehand, averaged across top players, just slower and worse. If you're not doing those things, you're not. That long string of "things to include" becomes one smooth natural feeling motion if you're doing it right, and you don't have to remember the bits once you get the feeling for a month or two. The off-arm is synchronized to the timing of first forward hitting hand motion, "announces it" and aids it.
I should announce my biases for you: I consider the "pat the dog" clue counter-productive, actually wrong. It's not what the pros are keying to, that's for sure. As you lower the racquet preparing for foreward launch, the point is two-fold: First, to get the hitting hand as low as needed for angle up to the ball that you intend, taking into account where the ESR will leave the racquet head. Second, to maintain a slower pace as you judge the incoming ball because, trust me, the instant you begin upper torso rotation, launching the arm while pushing a bit out with the hand as part of the ESR roll....everything happens very fast. That is perhaps the key beauty of the ATP forehand, that from the moment your brain says "go," and leads you to combine off-arm elbow pull-in with upper torso rotation, and instantly leading to ESR upper-hitting-arm roll, you'll be at contact in a flash. The initial torso rotation (the first 45º or so) can be made very fast, and transmits huge mo to the hitting arm/racquet.
Feel free to tell me which actions I listed in my third paragraph you think are not ATP, are left out by Federer or Nadal, or do not contribute something essential. Don't watch online tennis lessons. Watch the actual ATP players in action, slow-mo version. Do what they do (pick one player) as they do it in slow-mo until you've got the actions and the synchronization of off-arm and hitting arm actions. Really. Repeatedly, until the whole thing seems like natural smooth sequence. It's like watching a dance instructor. .......Otherwise, just listen to your new coach. There. The words are many but the actions they describe take less than a second once learned. My fingers are tired. Laugh. Best of luck.
