If you want to modify the base influence generation rate, then you'll want to edit ImprovementDefs.XML and edit the entry for the colony capital. The effect type to search for is InfluencePerTurn, defined to be 1.
Alternatively, I expect that you could use
<GlobalColonyMods>
<EffectType>InfluencePerTurn</EffectType>
<Target>
<TargetType>Colony</TargetType>
</Target>
<BonusType>(Flat or Multiplier)</BonusType>
<Value>X</Value>
</GlobalColonyMods>
to change the influence generation of each planet without touching ImprovementDefs.XML. If you use <GlobalInterColonyMods> instead of <GlobalColonyMods> you can get an effect where the value is mutliplied by the number of planets in your empire, but I'd suggest staying away from that for influence.
Something similar to the above is used to set the base value of resistance on the planet; look for an effect type of ResistanceBonus.
Next, you have several other constants in GalCiv3GlobalDefs.
- <InfluenceMinToClaim>0.03</InfluenceMinToClaim> is I believe the minimum amount of influence required on the tile for it to be displayed as being under your influence. I suspect that this is how the game decides how to round your influence radius.
- <InfluenceRadiusRoot>1.75</InfluenceRadiusRoot> is used to determine the radius of each world's influence bubble. The computation is [total influence at planet]^(1 / [influence radius root]), rounded based upon the minimum claiming influence and the bell curve target divisor.
- <InfluenceBellCurveTargetDivisor>3<InfluenceBellCurveTargetDivisor> appears to determine how quickly the influence value decays as you move away from an influence generator (most commonly a planet).
- <InfluenceFalloff>-0.6</InfluenceFalloff> I have no idea what this does. When I last checked, I did not see any obvious correlation between the influence decay as you move away from an influence generator and this number.
Hopefully this helps.
