That’s how I like to do it. I know it’s backwards to the way most people think of it.
So really I do it under this type of assumption (using Nick as an example)-
If Nick accelerated all out he could hit very close to his top end speed by about 32m. If we gave him to 35m using that same all-out run-in he could definitely be at top end (I’m pretty certain given our current training his fastest 10m split in a 60m race would come between 35-45m). So to make sure we can get more time in the workout spent in those precious 1-2 seconds that an athlete is at top-end speed, I throttle down the acceleration to just below maximal so they are less fatigued by the run-in and can perform an additional 1-2 more reps without significant losses in quality. Basically, I’m shifting the emphasis to top-end speed and taking it off of acceleration for that day because he’s told not to redline it during the lead-in to the all-out portion of the run. If he were to do all the reps with the run-in being at maximal intensity his efforts would be taken away from what I’m trying to emphasize in the workout.
The easiest analogy I can give is with a car. Say you’ve got a car that can hit it’s top speed of 100mph in 9 seconds if you floor it. Doing so is possible but it burns a lot of gas to do it. Because I’m more concerned about what the car does at 100mph than how it got there, I let you take 11 seconds to get the car up to 100mph. Not much of a difference but enough that you’re not burning through all your gas on the part of the run that isn’t the focus and can run it 1-2 more times at 100mph.
The examples I gave earlier are you close to A or B:
A: ACC to top speed to the first cone then maintain (relax, stepping over opp knee etc) through 20m fly zone.
B: ACC to the first cone, when you arrive at the first cone acc to 5th gear etc for the fly portion.
Sounds like you are more towards B..