I don’t look at if at all for my endurance stuff but looking back at my last season it tended to sit somewhere between .5 to .8ish.
Indoors: 0.63 for longer 2+ up to 4hr& 0.65 for 1.30-2hr. Never doing Z2 less than 1,5 hr
Outdoors: mostly going be feel checking HR, although the powermeter is equipped, usually it is 0.65 or less, but sometimes when I ride with someone else, for some (unknown 
) reason it still tends to be around 0.68
It’s an endurance day on the calendar but life happened and only have an hour to workout. You had intervals yesterday and threshold tomorrow. What you doing?
I’m wrestling with something similar right now. I did Ferreira (sweet spot 8.7) last night and I have Picket Guard +2 tomorrow (threshold 5.3), with Slatna (endurance 2.1) today.
Two hours at 0.53 IF is mind-numbing and feels a little pointless, so I’m trying to decide between skipping and put the extra recovery towards the threshold workout, or replace it with a higher IF alternate but have more fatigue tomorrow.
Between 2 hard workouts and considering that “life happens” is kind of stress anyway, I would do a recovery ride for 30-45 minutes with IF no more than 0.55
7 hours today with IF 0.61
I‘m also around a low 0.6 IF, a bit higher outside. An easy day, even with 4 hours of cycling, should feel easy at the end.
It feels like I even recover from the hard efforts during this easy rides. Sometimes it feels a bit like magic.
It‘s different with these unstructured 4h-summer-rides with efforts, these are in the middle.
Had to go look it up, but my last couple of 90 min zone 2 rides on the trainer have been at about .61.
Really hard to answer everything without writing an essay, but I’ll try.
Why? Because I was targetting really long events, but was running out of gas earlier than I hoped/expected. I also did gas analysis testing and discovered I was a big carb burner, really poor at fat burning.
I started by doing a lot more Z2, working out my individual Z2 upper and lower limits properly, and trying to maximise the time I trained in Z2. I also did a lot of fasted training at the start, but looking back, I am not sure this was necessary and wouldn’t recommend.
Looking back, I think the best things I would suggest (or would do again myself) is to 1) work out individualised zone boundaries; using generic % of FTP doesn’t work. 2) set a weekly Z2 target, and make that my #1 priority. My goal was 12h. YMMV. 3) do it all in a way that helps me ride consistently and makes training fun/satisfying/motivating, because long-term consistency is super-important. Maybe a bonus 4) Find the top of LT1, and don’t be afraid to spend time pushing this up (just be honest - don’t ride at tempo and call it LT1)
Does working over threshold lower LT1? This is a hard question! “Yes” - because every bit of training we do is a choice, and if we choose to ride above Z2, that’s time you aren’t spending at Z2, and generally there is a higher recovery cost to Z3 and above. But in real terms, going out on a group ride that is motivating is also important; or doing some tempo intervals, if that’s your thing. I think that if training 6 days per week, doing some intensity one or maybe two days is going to have very little impact on LT1 if your focus is on improving LT1 and achieving hours at Z2. Hope this helps?
tyty!