Interesting, I've certainly had nuisance trips at <100% looking at https://www.ece.uprm.edu/~lorama/Square%20D%20CB%20Curves.pd... page 36 you can see even at the rated 25c ambient it goes below 1 (though not as low as 0.9, much less 0.8 rule of thumb).
I haven't given it a lot of research because NEC requires 125% (1/.8) for continuous loads (for conductor protection).
I haven't given it a lot of research because NEC requires 125% (1/.8) for continuous loads (for conductor protection).
Perhaps my experience was hot ambient/panel.