Having 3 lines of level 1s is stupid imo. Line of level 3-4s and some backup here an there where you expect someone to breach them eventually will do better.

Case scenario - you are Spain and you are not friendly with the blue menace.

Option one - 4 level 4s at the bordering mountain provinces and 2 behind them for ZOC.

6*4 ducats = 24 per month

Time needed to siege - 300-400 days per fort with enough canons (20) and units (24). IF France commits 4 siege stacks the attrition will bleed them dry of MP, if they siege 1 by 1 it will take ages.

Option 2 - 24 level ones in all the provinces that are near the border.

24*1 = 24 per month

Time needed to siege level 1 - 30-60 days (tops if there is no breach early and the AI loves to assault low level ones).



We are comparing high attrition vs low, very big siege stacks vs peasant mob required for the siege to progress and time it takes for all the sieges to complete (1800-2400 vs 720-1440) caused by the added modifier to the low level fort siege progress.

I`ll pick 1 over 2 any day of the week