It might be worth putting a very short length of cable between the fuse and battery post. IDK I’m just a guy

I wouldn’t be that surprised if it was fine. Much of the time inline devices like this are designed to sink heat into the cables, and I’ve definitely seen some fuses that get pretty warm from being run more than 50% of their rating. They kind of have to in order to work; it’s not like the fuse can remain perfectly cool at 300,350,399A and then immediately melt at 400.