What is the logic of fleet groupings in Endless Space: Disharmony?

As of the Disharmony expansion, I've noticed a discongruity between the fleets and fleet power I can see from the planet perspective and what appears once I hit the button to engage a fleet.

It used to be that you hit the attack button, and your selected fleet squared off against their strongest fleet. Now, it seems, it still selects that fleet, but sometimes there are additional ships attached - almost like the individual fleets from the system can squadron up to some extent. The fleets appear distinct afterwards, so this would break the rules as presented to the player, who cannot split fleets except by disbanding.

What will tell me, when I look at a set of enemy fleets in one of my systems, exactly the group of ships I'll face when I attack?

Solution 1:

I've seen this happening but it works both ways, the AI isn't cheating.

The defender automatically brings in other groups up to the command point limit. These are whole groups only and after the battle they will still be separate groups. I've never confirmed pure ground pounders being brought in this way but neither will I say it can't happen.

Humans are generally sensible enough to keep their fleets full so you normally don't see it. I had a case where there was an enemy fleet I couldn't harm. I kept it pinned down by feeding it tons of scouts. I originally tried feeding individual scouts but it engaged them en-mass anyway. I found the most efficient way to do it was to blockade the system with fleets consisting of (Max CP/2)+1 scouts each. They would not combine.