From my observations of influence changes to date (assuming no other states are active, or civil war cooldowns present), when one faction surpasses another faction's influence their influence values will automatically be equalised, as in the image I've linked above.
You'll note that Faction B's influence was increased simply to ensure that it's equal with Faction A. I know you might think that other people traded with or supported Faction B to increase their influence for that day but that's not the case. You'll notice that the upward trend for Faction A continues, resulting in a shared decrease for all other factions. (This has been observed in several other systems)
This brings me to HR 7327, Dukues of Mikuun (34.4%) have overtaken HR 7327 Dymanics Commodities (31.9%) today. Yesterday's values were:
Dukes (33.2%)
HR Dynamics (34.2)
I expected influence values to equalise and "civil war critical" to appear as a pending state but this is not the case. Maybe this is because the only option available to expanding factions is "War".
War – Triggered by and invading minor faction reaching a high enough influence level. Decreases standard of living, wealth and security for the system while active. Influence changes only apply to the involved parties and are only applied from combat missions or actions.
However, this does not explain the pending "civil war critical" state that appeared for the Dukes in previous weeks. This implies that civil wars are possible for expanding factions.
Anywho, we have activities in another system involving an expanding faction and we're close to equalising influence levels with a faction controlling a station. We might be able to confirm similar results to HR 7327 in the next few days if all goes according to plan. There may or may not be a bug relating to expanding factions, we'll never know for sure until we can make observations in several systems and replicate the results consistently
Just when we think we learn something about the background simulation's mechanics, something unexpected happens and it forces us to re-evaluate our assumptions or makes us even more confused and frustrated due to inconsistencies caused by bugs!
