Dynamic NavMesh on Open World - fps loss

Dynamic NavMesh on Open World - fps loss

Even though the foliage trees do have collision how do I stop the dynamic navmesh from including them.

**1) In the static mesh what settings are best so that the tree is not considered an obstacle by the dynamic navmesh?
2) In the foliage selector what settings are needing set.
3) What settings will be needed for the navmesh box. **

If anyone has the right settings to remove foliage with collision from the dynamic navmesh then it would be very helpful.

Reason for Post
A 20x20 open world was working well but after I pushed the foliage instance count over 50,000 things started to hit the red
with massive frame rate loss. Remove the foliage entirely back to 30,000+ and frame rate recovers back over 60/70fps.

Ai still runs about happy as larry on the full 20x20 map without the foliage being in the way. So by logic and reason I hope it is
a navmesh issue. I tested 1,000,000 foliage instances on a different map with same setup and no loss was experienced. The only
addition is the dynamic navmesh and I need to cancel some instances on the foliage layer from its processing, but it doesn’t seem
as easy as I had first hoped.

Any pointers in the right direction is appreciated.

Its not the navmesh and I now believe it to be the collision on foliage causing the issues.

The limit reached was about 50,000+ foliage instances with collision. 20/30fps
Scaling back to 35,000+ instances resulted in an immediate fps improvement to back over 70fps.

Above: foliage instance with collision - removed from navmesh calc

Above: foliage instance with collision - dynamic navmesh

Above: foliage instance with collision - dynamic navmesh