Navmesh Agent

I would like to create a more random movement / path for my enemies in the scene. Currently they all spawn from the perimeter and begin to make their way to the center of the scene. However, since the Nav Mesh is picking the optimal path for all enemies, they end up grouping together and forming a kind of line in some cases.

While watching unity's official tutorial on Nav Meshes, he mentions you can add some inefficiencies to them where they don't all take the best route. However he never explains how to actually accomplish that, and just mentions it in passing. My search on Google has been fruitless.

Has anyone come across this type of "need" and found any solution?