I'm not sure what the size of the contact point is exactly, or how much leeway you have (obviously dependent on how close the OB is to the pocket). I would guess it's somewhat larger than you describe, otherwise I don't think any of us would make a ball. But I do agree it's a pretty small margin of error on anything more than a foot or two from the pocket, a few degrees at most.
I'm a recent convert to CTE/Pro1, after 20 years of "feel" or GB/track aiming, and I would say that while my percentage of long shots has gone up because of using CTE, and I'm still learning to have confidence in it, it's not nearly as much as the accuracy I've gained with short to medium shots. Two reasons for this - first and foremost, whether sighting a GB, contact point, or aiming line, it's still tougher to do at distance because the OB appears much smaller and the precision required increases because of that perception. Second, no matter what method you are using you still need great mechanics to deliver the cue ball where you are actually aiming, and at distance sometimes you see exactly how bad your mechanics really are...

For a player with mediocre mechanics, as with someone I briefly showed CTE to the other night, they can sight perfectly every single time but if they can't shoot straight it's not going to matter much.
Scott