One thing that you might want to look into. It seems as though the enemies aren't able to pivot. I don't know if you are forcing a constant speed which forces turns to be an arc or whatever, but none of the enemies ever just pivot in place. I think I ran into this before using Unity and it was something like that. Allowing the enemies to pivot in place will also allow for more fine grained pathing. as their turns aren't these giant arcs.
https://docs.unity3d.com/540/Documentation/ScriptReference/NavMeshAgent-angularS...
So looks like it's a function of speed, max accel, and angular speed. With absolute speed capped, max accel and angular speed probably aren't too concerning to set very high.
Good luck!