I've tweaked this for two campaigns now, but to a set amount regardless (just for challenge) of how many cities. Check out my Roman/Saka campaigns in the a.i progression thread to see a rough idea, at least for Ptolemaic/Seleucid progression. I gave certain factions in game cash bonuses and those are listed in the posts. I don't know how helpful this will be to you because it's a raw amount and not the variable that you have, but I hope it can be of some use. Also to note no rebel spawns and few pirate spawns.

In general it was: Slave was reduced to 1000 to keep them ok but reduce wait time for the a.i to get big. All factions were upped to 1800. Special help was upped to 12000. With the Ptolemies at 1800 and the Seleucids at 300, they got totally crushed in my Saka game, while with both at 1800 the Seleucids rolled over them in my Roman game. Well totally rolled over as in at 235 the Ptolemies had conquered Seleucia and the Seleucids had only taken two out of the 6 eastern territories available to them. In both they were still able to bully around the Saba though, even with them getting a 250k grant. Saba are at 18000/2700 even in my Saka game, so I really don't know how to help them.

This is purely conjecture, but from experience it seems certain factions simply have better a.i than others. The Getai, Saba, and Hai, as well as the Steppe factions, seem to be always hopeless even when I give them several hundred thousand in the first 10 years and 50% more income than the others in both ways. In my Saka game the Parthians were making Grivpanvers and noble cataphracts with their three territories but really didn't use their troops very well at all despite having over two full field armies. They tried attack Bin-Kath and Gava-Maszakata each twice but for the most part sat around and did nothing; which end result let me defeat them with a 5-10 man army over a few years. Often times these factions just end up sitting around and doing nothing and giving them 100-400k+orders to attack the rebels doesn't do anything. Bactria has also been like this in my campaigns in general. They didn't do anything in my Saka/Roman ones, just sat around with two big armies.

The Romans, Carthaginians, Greeks, Luso, and Gauls are in between. They can get big and can flounder. The Greeks have a problem of being stuck in war with each other for potentially a long time but if one conquers the entire hellenic area they expand very fast. The Romans generally do well as long as they can kick Epiros out of Italy. The Luso do nicely if they win against Carthage in Iberia and die otherwise, whereas Carthage would be fine if they simply didn't fight at Kyrene and could manage to ship their troops places. Usually they just end up being stuck somewhere where they aren't needed. The Gauls have early war problems like the Hellenics but they do fine if one of them reaches an early supremacy.

The Ptolemies, Sweboz, and Seleucids seem excellent at using their troops, it's just their Ptolemies get into wars with Kyrene and are outmatched by the Seleucids and the Sweboz have a tough start. But the Sweboz seem to either to great or flounder horribly. Every campaign I play/see them get to a decent size they just keep on growing and don't stop, especially eastward, but if they can't get on their feet then they just sit around and die. Pontus usually does that but when I gave them 50% more income and a 300k grant they managed to take some cities nicely and have a 6-7 large northern Anatolian empire in both.

I don't know if this is relevant or not due to possible changes, but in my .80 Macedonian campaign the Ptolemies had their armies mostly of agema or galatian heavy infantry troops in 215 whereas the Seleucids were still using mostly mediocre troops despite having 45 provinces. Only a few times did they use TA, Argyraspidai, Agema, or Cataphracts. The Bactrians with 25 provinces only were using medium infantry at the best and had very little cavalry.

I don't know very much about how the a.i works and what is hardcoded or not, so I can't really change anything to test it. But it would be very nice to make a.i factions in general more aggressive to each other, not just to the human who takes one of their starting territories, and to make them produce more elite units when they have the access money to it.