My understanding is what you wrote below: most coaches aim for blocks that are 4–6 weeks long, and that coaches play tetris, i. e. they see what fits. Personally, I like 4-week blocks, but I occasionally do 2 x 3 = 6 week blocks. I cannot speak for anyone else, but I think staying in the rhythm of structured training has more benefit than looking at some metrics.
I’d say that depends on what you/your coach has identified as goals for the season, and whether fractional utilization is important for reaching these goals or a useful metric to quantify progress.
E. g. a multi-year approach where you alternate between raising your VO2max ceiling with e. g. a training plan that focusses on short power and repeatability (think Crit Plan) and a plan that broadens your base (Climbing road race, XCM, etc.) sounds like a good strategy.
You wrote earlier that your FTP-to-MAP ratio varies significantly within a season. I think this is a very astute observation, and shows how much experience you have as an athlete. While that sounds a bit surprising to me as I’d expect this number to change slowly once you are a few years into structured training, we are all individuals and some aspect of us is bound to be out of ordinary. Hence, if that’s the case and it is a concern of yours, then I’d definitely continue keeping track of your MAP/power at VO2max and your FTP. That means you’d have to do a ramp test every now and then, and find some way to measure your FTP (you could use workouts to validate it or some other FTP test protocol).
Before altering your training, I’d probably watch what happens over the course of a season and try to discern any patterns. E. g. my body reacts differently to a polarized base block than a sweet spot base block. Neither block is “bad” or “better”, it just depends on my goals which block suits my goals more. So think about what goals would benefit your riding the most. Some people focus on TTE, but if e. g. you are a crit racer, that’s not a productive goal.
Then you could adapt your training accordingly. If you e. g. want to increase power production, you could alternate between blocks aimed at raising your ceiling and those that increase your fractional utilization or TTE at threshold. Of course, that is assuming this is compatible with your goals for the season or across seasons.
