How to get more than 2 defenders spawn from a farm? (Kremlin is present)

[ZenDen]

Hi everyone!
When the Kremlin is installed on the base, when a farm are destroyed in battle, 2 infantry defenders are spawn. In PvP when attacking some bases I see the spawn of 3 defenders.
Please tell me how this is possible? What needs to be researched or improved?
Thanks!

 

[Wayne]

Research: Heritage Chapter 3 in Library in order to get +3 defenders from destroyed farms.

 

[ZenDen]

Research: Heritage Chapter 3 in Library in order to get +3 defenders from destroyed farms.

Many thanks!
I thought about this book in the Library, but decided that 10% was not enough for yet another defender. Apparently, it means more "at least".