I'm actually talking about something more 'proactive': the AI has probes (or it just knows) to find out where human FP is concentrated and then attacks that area. It has to make decisions as to how to distribute its own FP to attack but the player might make that easier by having a fleet ball in that sector. Special forces shouldn't be 'special defenders' but rather the AI's tactical response to player concentrations of firepower.
We already have a system that says Warp Gate = attack and there's no way that the AI could win if it only used that feature. CPAs tend to attack random regions with some disruptive force (attacks on power and resources) but there should be a mechanic that attacks the player's offensive capabilities on the player's own planets.
Personally I fleet ball and think that it's fine-- as a history student I have to say that an AI programmed by humans would think either on a Clausewitz principle of 'destroy the opposition's ability to resist (ie army)' or OODA (observe, orient, direct, act). I would certainly want to destroy the human ability to resist in either case (maybe an AIP value for this behavior).
There already is a feature where the AI will choose which planet to target based on firepower, threat fleet. However, threat fleet tends to choose planets with the
least firepower, as it is the least likely to get curbstomped by a big "ball" of stuff on the other side and live long enough to do actual damage.
The ultimate problem is that if the AI is trying to take out human concentrations of firepower procactively, it would need absurd numbers of ships to be able to reliably take them out, and crazy numbers of ships to assure decent economic damage. I mean, if you can shrug off 2000 fleet ship waves (which is rather easy to set up a defensive system that can), would 3000 fleet ships from wherever really have much chance either?
I suppose that those extra ships could wait for the next wave, and then head on through when it comes in, if it determines that these together would be enough to have a decent shot at taking out the planet (or at least severely wounding it). (All the various "should I go in?" considerations already take this into account, so no new logic would be needed)
Now, I am all for expanding the special forces some:
Things like allowing the special forces to "split up" (so they don't all wait at the same place, but different groups can wait at different places).
Or treating a "planet under significant attack" (aka, a blob) as a planet worth defending (though not as high priority, and certainly not all the special forces as that would make it too easy to bait).
Maybe even have a mechanic that once special forces gets really large (near the cap), some of the special forces will "break off" and be put into threat fleet mode, joining up with the other ships "planning" a strategic offensive strike, slowly leading to a rather large amount of stuff seeking out your "weak points".
Whatever is done, care should be taken such that it wouldn't be trivial to bait the AI.