allie bounus

at $100k, found that plunder bonus = .0048 x hire cost. at $81k found bonus = .0045 x hire cost

 

If you have 1 million attack bonus from allies, it's 20k attack

 

1/50 or 2%

 

After a bit of study this is best I can tell ... U take the max plunder bonus (listed on your profile), and multiply by 100. The resulting value is the necessary total 'hire value' of your allies if u want max plunder on attacks. The build u have has some influence, but the 100x rule seems to work in most cases for me.