Starting line beams are usually right at 1.5"+-. The top end beams are generally 6"+-. The Rulebook has a 3" minimum rule to make sure you clear. Means nothing about how high the beams are. If the rules allow a pecker extender then why not take advantage of it. Some of the new late model cars have 40" of front overhang on them. Meaning when you leave the have an immediate 40" advantage on cars like a Dart that is not in the weeds.

I believe the NHRA's current stance on pecker extenders is they are not legal. They are only allowed to be even with the farthest point forward on the car, ie the leading edge of the front bumper. Many many bracket cars use stripe takers on the front end. Once of those things you need to pay attention to in the lanes for sure.