I worked with a guy yesterday who started doing the Hogan "T2T" move during his backswing a few months ago. Initially, he started hitting better shots, however, as time marched on he started hitting fat and thin shots. He didn't understand why the T2T move, which worked SO well in the beginning, suddenly stopped working for him. Then he started saying maybe S&T doesn't work for him...blah blah blah. LOL.
Upon watching his backswing, it was obvious he was over-doing the T2T move. He was shifting his lead hip about 3-4 inches towards the target. This move caused his lead knee to travel laterally, or towards trail knee to the top. Then when his lead knee straightened on the downswing, he created a reverse pivot which moved his swing arc to his trail side, or what Tom calls the "Zone of Death". Any time I start hitting thin or fat shots my first thought is "my swing arc has moved to the right...why?".
In the early stages of doing T2T, most folks move their lead hip just a little because it's a new feel, different move. But after a while the body gets used to it, thus it becomes much easier to start over-shifting the hips towards the target. I got in front of a mirror and purposely threw my lead hip too far towards the target to the top, then looked at my lead knee position. It moved 2-3 inches laterally towards my trail side. Thus, my lead knee position was more "underneath me", or my lead knee was buckling inward. Posting up from there moves the swing arc to the right. Then I did a "little" T2T and my lead knee bent down towards my lead foot, not towards the trail knee. Check.
Watch Tom's video below. At about the 7:00 mark he presets his trail leg straight at address. But during that demo, his lead hip moves a little towards the target, not a lot. He's not "throwing" his lead hip at the target like the guy I worked with on the range. Also note that in his preset position his lead knee bends down towards his lead foot. It does not travel laterally towards his trail knee.
https://www.youtube.com/watch?v=RZUKFguEJc0&t=361s
@GolfLivesMatter - Yes, that preset position is what I've referred to here as the Elkington Setup. Even though this lesson is in the Limited Mobility section of the school, it can likely be of some benefit to the gentleman you were assisting.
Nice call on the effect of overdoing the T2T!