Ok, currently:
FallenSpire_SpireCityHub has
IncrementsEventWaveCounterByThisPerMinute = 1000
AddsThisToMaximumEventAttackThreshold = 60000
FallenSpire_SpireShardReactor
FallenSpire_SpireHabitationCenter
FallenSpire_SpireShipyard
(all three have zero for both variables)
FallenSpire_SpireGalacticCapitol
IncrementsEventWaveCounterByThisPerMinute = 1000
AddsThisToMaximumEventAttackThreshold = 60000
and then there's the last-phase structure, but that's not in consideration here and not part of a city anyway.
Anyway, I'm thinking that the way the max threshold is computed shouldn't change, as if it started going up and down on any kind of frequent basis strange things might happen.
But I could change the IncrementsEventWaveCounterByThisPerMinute on FallenSpire_SpireCityHub to 250, and give FallenSpire_SpireShardReactor, FallenSpire_SpireHabitationCenter, and FallenSpire_SpireShipyard all 125 so that a fully built city (6 structures + hub) would still generate 1000.
The hub itself still needs to have some, as building a city is supposed to be an irrevocable escalation, etc, etc.