Let's start with your 1st sentence in the main paragraph. So, a racer is cutting consistent shit/slow RTs or red lighting. I know I'm going to make changes to the race vehicle(s) set-up to change the RT!
Now, for the second sentence. There's only one time a year I set up for a perfect RT. We have a 50K run for the money. A perfect package wins, we set-up for a .000 RT. The rest of racing against an opponent we don't shoot for perfect RT. Reaction times have a variance based on different factors. We try to keep that variance as tight as possible:
Let's use a .010 RT variance for testing/qualifying. During racing if I set up for a perfect RT. The RTs are going to vary -.005 - .005, going red isn't going to work for my racing.
Now, take that same .010 variance & set-up for a .005 RT medium; you theoretically get RTs in the .000 to .010 range.
I do agree with staging shallow as possible to keep RTs & ETs the most consistent.