Starsector 0.97a is out! (02/02/24); New blog post: Simulator Enhancements (03/13/24)
Wyvern is 100% correct about the math.
So, I'm waiting in orbit for an expedition to show up... and I see several of the merchant fleets that came to deliver cargo fighting amongst each other. This seems... incorrect, even for factions that are hostile. Plus I'm not really looking forward to the possibility of shortages or accessibility penalties just because two at-war factions decided to send cargo haulers over at the same time.
They generally don't attack each other, but will fight if they get in each other's face. Jostling for prime orbital positions getting out of hand and all that.
Either way, though, that shouldn't affect your accessibility (which is only affected for the colony that sent the fleet), though it might cause a shortage.
Hm. Not quite the behavior I was seeing - they definitely went out of their way to attack, with mouseover tooltips showing that they were in active pursuit of each other. It's possible that this was a mod-related issue, though, as both battles I saw involved (different) mod factions.