Base cost:

2% per system

20% per planet



Current situation:



Suppose you have 5 colonies & 50 systems. Costs are x2 from colonies and x2 from systems, giving a total increase in unity costs of x4



If you now add an extra colony, that colony does not only increase your unity cost by 20%, but by a total 40% (!!), since your amount of systems doubles the cost for each additional planet.



Same goes if you'd wish to add an extra system, not just a mere 2% increase in costs, but a nasty 4%



Just imagine having 100 systems and 10 colonies: Costs are x3 (colonies) x3 (systems) giving a total cost of x9. Each additional colony costs 60% more base unity.



50 systems, 5 colonies = x4 cost

100 systems, 10 colonies = x9 cost

150 systems, 15 colonies = x16 cost

200 systems, 20 colonies = x25 cost

450 systems, 45 colonies = x100 cost



Problem:



This increased the costs for additional planets in the later game exponentially, having both many systems and many planets will make late-game unity gain effectively zero in bigger galaxies, or very slow in smaller ones.



"Solutions/Results":



- Stockpile unity (don't spend) with many planets (for high net unity production), then release a load of vassals to reduce costs and buy all the traditions.

- Go with the easier vassals civic, and keep down number of planets.

- Stay medium size, until 2300/2350 when you've bought all traditions.

- Stay small in number of planets or number of systems to avoid multiplicative costs.

- Just ignore unity and maybe even tear down all unity buildings once you've gotten 3-4 tradition trees, depending on when you get too big.

- Mandatory expanders (like the genocide guys) will probably get in trouble if they focus too much on unity gain.



Extra note:



- Science costs don't get multiplied.