Irradiance is the function of stellar luminosity at a given distance. I must ask if 80% is the barrier at which chlorophyll becomes competitive with Purple. The very graph of outgoing radiation, in the 70s%, should be redshifted, nu? like with K? We know the Archaean had no ozone.
I might allow indigenous chlorophyll wherever a stromatolitic planet hits the 80%-irradiance mark. That can be at 1.1-Gy rather than, as here, 2.1. K and G planets once habitable stay habitable, for billions. Albeit fewer billions for us G inhabitants; for our part we've wasted at least one Gy, and since then arguably had an extinction-event too many. εEridani is still too young by the way.
This further opens up F stars in distant orbits which, note, aren't T Tauri for long; so allow even more volatiles than we do. "But Chicxulubs!" - the impact velocity of that semimajor of (here) mushy asteroid will be less, 2 AU out (although we'll need to constrain the number of longer-period rocks).
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