DoN's 3D-Pathfinding / Flying-AI system (with full source!)

This may be a stupid question because this specifies that it is a flying AI system, but is there a way to query the system for land-bound paths and to prevent traversal of steep slopes?
I have a relatively large voxel world with player-spawned structures, and while navmeshes work I am looking for a more optimized approach for NPC movement.
The system would not have to handly many actors at once, pathfinding would only be activated when a player is nearby and actively being chased.

If the system cannot be used in this scenario I would appreciate any pointers for other options.
Thank you!