I can't really think of a better way of deciding in what percentage the map should be split.
Also, mirroring the map (which won't happen for now due to technical reasons) does not solve this problem, because the percentage would still have to make sense. Because otherwise one region would be way emptier than the other, and that's unfair for those who happen to be in the region that's packed. That might even force people to go to the other side, just because it's less populated, which renders the whole idea of splitting the map useless.
tl;dr: find me a better way to decide in what percentage to split strategus. But something that can be calculated, not just some gut feeling.
Strategus 2.0 was 3x more crowded than 1.0 and only growing more populated. Makign twicea s much spacea nd it would still be very crowded allowing for plenty of fights, but when you keep it his small it actually reduces the activity because only 1/5th the clans can have access to owning a fief allowing them a capacity to fight near equal parity with fiefed clans and eventually 1-2 alliances own most of the fiefs instead of a constant vying back and forth between many small clans across many fiefs more simialr to the first half of Strategus 1.0.
If you looked at the activity level and not just population you would note that NA community more active. My clan had 90+ battles in Startegus 2.0 and only 50 active members, whereas there were several EU clans that had 2x to 3x our numbers that might have fought 15-20 battles at most and most of those were against neutral fiefs because other than leaders logging into their members cd keys, they were mostly inactive players (just look at the account sharing thread, account sharing is rampant in EU).
So maybe look at how often NA members logged into Strategus v. EU players and not just the numbers. Basically measure how many hours NA community members were logged into Strategus v. EU (you can tell by looking at what their favored settings were set to).
P.S. Also, if doing a split make the West NA, this last version all the NA players were on the Eastern,middle, nothern, and Southern areas. If you dont change it up , all the EU clans thata re boring will just go back to their "ancestral" and highly predictable claims instead of actually fighting. Whereas NA will fight regardless, those EU clans might actually fight when they dont have set lands to claim anymore and its more of a first-come first-serve basis.