That's right, TOI is effected by the shot speed.
There are three basic calculations we have to make on each shot.
The shot speed, the cue ball target and creating the correct angle.
Many players separate these three and play different speeds, mixed with different cue ball targets (where you contact the cue ball with the TIP), and different contact points.
When a player decides to go through the TOI training they will be required to blend these three together, using a consistent shot speed, with a standard tip target (TOI), and the angle created off either the center or edge of the object ball.
I rarely use more TOI, just a "touch" is usually sufficient (if anyone can tell I'm favoring the inside I'm probably using too much), so If I hit the inside of the pocket (where I'm aligned to) the very next shot I'll increase my shot, which cuts the object ball slightly more.
When I see a player undercut a shot, I watch to see if they do it again. Even if they make the shots I know they are not calibrating towards the center of the pocket. It's probable that the closer they get to winning the game, (or the match) the more likely they will undercut the shot even more and miss. This shakes their confidence because they won't know why this happened.......and I'm certainly not going to tell them.
To perform well over a period of hours there must be a way to continually calibrate where you're hitting the pocket. This is not possible using center ball, if you increase your shot speed it will exaggerate any deviation in your stoke, not help force the object ball in a predictable way like TOI does.
I was talking to a top notch golfer last night at 'Diamond Jims' that has made his living gambling (he lived in Vegas for years). I ask him, "when you're betting high, do you move the golf ball in both directions (draw and fade)?"
He said "hell, no, I'll hit a fade, even if there's water on the left because I know my natural swing will move the ball left to right". He went on to say "Lee Trevino is the first one to tell me this, it made sense so I've done it ever since" (Lee was known to be an almost unbeatable golfer at Tennison Park Golf Course in Dallas).
TOI is the same principle, it's reliable under pressure because you always know which way the cue ball will move off line if the shot isn't hit perfectly. Also, once your shot speed is calibrated, you can increase this under pressure and it will be even more accurate. De-acceleration is the reason most players "dog it," not over-acceleration.
Remember this, it seems simple, however, it's vital to overcome pressure situations. TOI or TOO practitioners have a built in way to continually calibrate their shots, is they understand how the pocket zone is created and approached.
TOO players create zones with deflection and spin, TOI players do it with deflection.
I can achieve this either way, it's just personal preference to use TOI so I can hit the cue ball slightly firmer. This works well on regular table conditions, under tournament conditions I have to adjust accordingly (using less TOI or more/less cue/shot speed).