[With_Two_Flakes]

When you saw the hold, were you stood still? I find that if I am stationary, it is tough to start moving again. The diagram is fine, but it doesn't show YOUR movement. Certainly you can and should look through the QB to help out with holds on the far side. But that is secondary since the QB is your main concern. You have to react to what he is doing as your primary key - he moves, you move.
On a drop back pass, I drop back as well to keep my separation and to keep on the move. As soon as he rolls left or right, I change my backward movement into sideways movement to try to keep the same relative position to him.

As others have already said, starting deeper and wider is better. I start 15yds deep. Back in the day I'd be behind the guard/tackle gap, now I line up two or three times as wide as that. I don't work as wide as I have seen recently on TV, but I do find that wider is better. The downside of being as wide as on TV is that a run play away from you leaves you trailing the play by a big distance. You have to remember that TV games (NFL, NCAA) have 7 man crews. On a 4 or 5 man crew that most of us work, the WH has to think a bit more about his sideline to sideline responsibility.

If you ever have this situation again, forget trying to get the number of the guy holding. I'll bet you already knew his position, eg left tackle. Don't get hung up on numbers on fouls and miss some other big stuff such as your possible roughing call. Being able to tell a captain or coach that it was the left tackle or right guard etc is good enough. That'll allow them to chew out the person who fouled.