Since the map for this level is fairly big and the essences are not marked, I spent a few minutes scrolling the minimap trying to find the other two essences to no avail (I did find the one closest to my starting base). Where are they exactly? Would anyone be able to pinpoint them on the map?
Basically the other 2 essences are in the north-east and south-west corners of the map.
Here you can see exactly where.