Just a few observations that I made when visiting the system today (I had a little time in between my tasks not far away).
There is indeed money to be made in massacre missions as you say, but be aware that piling on a huge amount of the same mission types isn't as effective as piling on a variety of different tasks such as those massacre missions, commodity sales (for profit, not loss), black box and salvage missions, deliveries, courier jobs, cashing-in exploration data, redeeming combat bounties, etc. Variety is the spice of life and is also the way to go for BGS impact.
After today's Tick and when the system updated, I noticed that the Quantum Whales' INF fell again (from 46.4% to 45.2%).
I did a bunch of courier jobs, hits, deliveries, etc., and became allied and contributed some tens of INF to today's tally for the Quantum Whales (perhaps 30). Maybe it will help...
Activities all reach a level of diminishing returns as you pile them on. Details for most of these (when / how much) are outside the scope of my BGS knowledge, however I do know that approx 100 million credits worth of cartographic data handed-in (per day) is where you reach that point of diminishing returns (for carto-data). This is the cumulative value of all CMDRs' contributions.
The Yakabugai System doesn't currently have any places to earn significant bounties from combat. If another system where they have control does, you can earn them in that other system and then bring them to the Yakabugai System and redeem them at the port where the Quantum Whales are in control. You can earn bounties in combat at CNBs & RESs.* This is an example of a situation where benefits are portable.
There are currently five fleet carriers in this small system. Depending upon their activities, they could have a huge amount of leverage on the faction-states in this system- easily far more than one or two CMDRs could hope to overcome. Perhaps you know or are affiliated with one or more of them and can find out...
Selling commodities to the black market in a port negatively impacts the controlling faction's INF. This isn't applicable at Serebrov (because it's shut down there), but it's something to be aware of.
This also means that you could sell black-market goods to cause another faction's INF to fall. Before you attempt this, please get clarification from a BGS-person to determine if you can do this by simply selling at the black market in another port that is controlled by a different faction (within the system, of course). I'm not entirely certain, but I believe that's all there is to it.
Redeeming bounties for other factions at any port in this system hurts the Quantum Whales' INF, so this is to be avoided.
Trading goods (profitably) or cashing-in cartography data at stations (in this system) that are not controlled by the Quantum Whales benefits those other factions, so this is to be avoided.
Random traffic (other un-interested players passing thru) and their missions / trade activity all counts too. This can make it really difficult to have a grasp on what's happening in busy systems, not to mention moving the faction states in a desired direction.
It remains to be learned what would happen to the Quantum Whales' INF and position if things were simply let go the way they may. I certainly understand if you don't want to learn that, of course.
This is a native faction, so it cannot retreat from the system. Its place is secure at least in that way.
*
CNBs = Compromised Nav Beacons
RESs = Resource Extraction Sites (incl Low RES, High RES & Haz RES)
