FWIW, you can refer to many different sources and get different answers.
For example the ABYC E-9 (for boats) has this suggestion, which is the primary basis for the Blue Sea calculator. SAE and NEC have different set of rules deriving from a different set of assumptions and requirements.
I've done some work over the years calculating it based on fuse curves and heating of wire for times from 60 to 900 seconds based on type of insulation. What I find is my comfort usually falls between the NEC and the conservative ABYC ratings, so your manufacturer might be following their inside engine room allowance.
NEC is conservative IMO, probably because their primary concern is lower risk of fire. Their assumptions are electrical distribution and premise wiring so they have different cooling concerns and how long a fault might exist and different tolerances for cost and weight. If you follow NEC you will be more than adequately safe.
View attachment 524781