I'd guess the higher temps just edge stuff closer to their failure point. On really hot days, the cooling fan flow feels much like a heat gun.
In my application, the controller will turn the fan on anytime the AC clutch kicks in. Every time I've checked that, it seems the fan is in high mode. These are "hard" starts when compared to engine cooling where the fan starts in low and switches to high at a certain temperature; that gives the high side a running/soft start as the fan is already turning. I think the current spikes from the hard starts might be the major factor in the fuse holder heat. I could disable the AC clutch input on the controller, but I do like how quickly it makes the AC blow cold before getting up to speed or before the engines warms up enough to kick the fan on.
Regards,
Greg