For most people, 6X60 is the whole workout–there’s a chart in CFTS about the amount of speed to do in a session. What else you’re doing might be part of the issue.
There have been a number of threads in the past discussing acceleration limits, for people not able to accelerate for the entire distance. You put a cone at, say, 40 meters, and accelerate to the cone, then maintain. As you get in better condition (over a season or a career) and can accelerate longer, you move the cone out.
You can use a more gradual acceleration for flying sprints–or hold something back coming out of the blocks to produce the same effect–but it is not the only way.
I’m not sure if the total volume is the issue or if you are pushing too much in the accel part and losing form the farther out you go (I suspect that’s the most likely cause. Make sure in the acceleration you keep the ‘action’ under you and not behind you.
As Charlie pointed out, these are Guidelines, not rules, but I’ve found Charlie’s guidelines to work very well for me. You can find them on page 42 CFTS, with recommended numbers of reps for 30m through 80m.
I should have mentioned that it is page 42 in the PRINT version of CFTS; The “page” of the .pdf file would be something different.
When you do more gradual acceleration, you (should) reach a higher top speed. But the more gradual accel progresses more slowly and is done longer (time and distance). So if your hard accel is 30m, your more gradual version might be 40m to reach a higher MaxV. This really what flying sprints are all about. Possibly the reason you didn’t see an improvement with the more gradual lead-in is that you didn’t go long enough.
As for mixing accels and flys in the same workout, you can if you keep the volume in the range that gives you maximum performance. Early in the season, with the emphasis more on accels, you might do 3X60+2X30 fly with something like 10 minute rest between each. Later (maybe early in GPP2), the emphasis might be on MaxV and you can turn the workout around: 3X30fly + 2X60 accel, which probably the same rest.
It would probably help more if you did a flying 20 or 30. You’re clearly traveling at a set rate of meters per second (max velocity) whether you hit it hard or gradually work up to it. If your flying 20 falls off from your flying 10 time then we could look at other things. Ie 10 fly 1.06, 20 fly 2.26. You follow?