For an IF of .45 that would put your FTP at ~375W. My FTP is ~250W, during normal training and following a hard bike workout + weight lifting, a recovery ride would be around 80W or an IF of about 0.3.
And to answer the “how low can you go” question I have this blue ribbon effort with an IF of 0.19:
seriously if you ride hard and lift heavy on say Tuesday, doing an easy recovery ride on Wednesday will only help you feel better. But it has got to be REALLY REALLY EASY. Less than 100W easy. You can’t go to low. For context I’m averaging 7-8 hours/week this year and have a coach.
The other time to do recovery rides - after a season break. Right now I’m easing back into training with 2 weeks of recovery rides. This is the only time of year I do rides by HR. Here are a few from week 1 of returning to training after 3 weeks completely off the bike:
Last night I was up to an IF of 0.47 
Strava ego busting average speed for those 4 rides:
- 9.8mph
- 11.2mph
- 14.1mph
- 13.1mph (windy)
First one HR at bottom of zone1 and ended up with an average power of 47W After that I pulled HR up near top of zone1, my Strava ego simply can’t handle sub 10mph rides LOL.