I was doing a lot of sweet spot work beginning of this year with goal of really extending time in zone. Believe my profile is open, you can see the work I was doing end of December and January.
It was all progression of gradually building interval duration and worrying less about driving power up - holding 88-94% for longer periods of time. I would say doing the long FTP test protocol Kolie Moore FTP Protocolsets you up well to establish your end goal time in zone.
Example - FTP of ~300 held for 35 minutes. By the end of a block I was aiming to accumulate 200% of that FTP time (70 minutes or so).
Was a progression of 3x15’ > 3x20’ > 2x30’ > 3x25’. That progression was over the course of about 4-5 weeks. Then moved on to a similar progression at FTP.
I haven’t had nearly as much time to train as in the past and average around 8 hours per week - so slightly higher than mid volume but you could cut the endurance rides down.
Hope that’s helpful
Edit: basically what @jarsson said…perhaps I should read the whole thread first 