Tami, you are correct. I use a delay box. But I think that was easier to figure out because you know who I am.
I started out in nobox though. No matter how you control the launch of the car, some things are the same. Mechanically, the car must be staged the same every time. Physically and psycologically the driver needs to be have same level of tenseness (sp) and mental state every time. Stiff and tense muscles react different than relaxed muscles. Excited and bored result in different reaction times.
The pratice tree enables a driver to work on many of these things. While practicing I concentrate on not being tense. For me this means not holding my breath, keeping the body relaxed but not lazy, and blocking out my surroundings. Believe it or not, I still practice bottom bulb on occasion. No matter if it is top or bottom bulb, my routine is still the same. While it is true that top bulb is easier to be consistant at, both have one thing in common though. That is anticipation. Anticipating the light happens in both. Some say that it is impossible to anticipate the top bulb. But believe me, it happens. If your mind isn't focused on making sure you see the light flash and you are trying to release the button as fast as possible you can be varying the tension on the button and as you are lessoning the tension (because you think the light is going to flash) the light comes on and you release. This will normally net you a red light, assuming that the box is set for a .00x and your routine is consistant any other time. The same thing happens on bottom bulb. Except, it's worse because you can watch the tree come down. If you are footbraking, its your feet reacting different instead of your hand.
Once you are consistant, most likely, you will be able to guess what you reation time is within .01 or even know if you fouled before you get your timeslip. I've always been aggressive on the tree and have lost many rounds with -.00X lights. With the aid of the bump up feature in the delay box I have only had 4 redlights during eliminations in the last two years. I can just "feel" when I have slightly anticipated the light. I can leave the box on kill and protect myself against the redlight with the bump up feature. With that being said though, I can only recall using the bump up about 8 times.
Have you ever heard someone say that they can be great on the practice tree but suck while in the car? Barring any car problems that can cause inconsistancy (there are many) the problem is probably because they stage the car inconsistantly and don't have good data to create trends by, and therefore can't change the car or the delay box correctly. Or, though less likely, they do not keep themselfs at the same level of intenseness and muscle tenseness.
Sorry for the book, just giving my input based on 12 years of experience.