The text is not clear on this - it can either mean "effect will be distributed only to all aligned minor factions" or "effect will be distributed to controlling factions and all aligned minor factions".
The latter would make more sense because systems can and do have no aligned factions for a specific power at all.
you can't cash in superpower bounties where no faction alligned to that superpower is present, though (beside interstellar factor contacts)
We are in a system with 10 billion people and the most I've seen is a 2.5-3% swing in one tick
sounds about right. but:
to get this correct, you'd have to think in +inf/positive influence for a faction, and +inf/influence gains via distributed influence losses of other factions.
which means: my own experience is you can get a maximum +influence by actions for a faction (missions for exampel) of 15% in a 60k population system. but you cn gain much more, if you combine that with hurting other factions in the system.
let's assume we have faction A, B, C. A: 40%, B:35%, C:25 % in such a system:
A gains 15% by missions running A = 55%, B=26 %, C=19%
B looses 15% by black market trade. B=11%, A=66 %, C=23%
C looses 15% by ship kills. C=8%, A=76%, B=16%
so, while the cap is around 15%, A would gain 36% over night (and that assumes, that the same cap is on negative as on positive influence swings, which isn't the case imho).