This is a side-effect of the choice of node locations for the A* search. It's a bit unfortunate and does happen a fair bit, especially where there are large polys next to small ones. Mikko wrote a little bit about it a long time ago here: http://digestingduck.blogspot.co.uk/2010/08/navmesh-node-locations.html

What I suggest is decreasing the max edge length, which splits up long edges and results in polys being similar sizes. It does mean your navmesh will have more polys, so will be slightly less efficient in many ways.

Something I personally found to work slightly better too is tweaking the pathfind to put node positions in poly centres instead of edge midpoints, but this is a bit more of an involved changed and still suffers the same problem often. Change this bit of code in DetourNavMeshQuery.cpp to create the node position at the poly centre:

        // If the node is visited the first time, calculate node position.
        if (neighbourNode->flags == 0)
        {
            getEdgeMidPoint(bestRef, bestPoly, bestTile,
                            neighbourRef, neighbourPoly, neighbourTile,
                            neighbourNode->pos);
        }

Lastly, what I ended up doing on another project, was to run a pass over the path to raycast along the navmesh between pairs of points, replacing parts of the path with more direct results if found. It's expensive but does produce nice paths (but again, isn't perfect!).

another trade-off could be to raycast only between start and end position and fallback to usual pathfinding with nodes if end position is not in line of sight.

Also look at DetourPathCorridor.cpp. It contains some interesting optimizations, and I believe some of them deal with this problem.

A typical way to deal with your problem here is to continuously optimize the path by trying to raycast a few polys ahead, i.e. 3-4 polys ahead, and then skipping the polys in between if there is a straight path.

I believe Mikko has written about this in a blog post some time ago, but unfortunately I cannot find it. You can try to look for blog posts that may be relevant at his blog.

Hey @1vanK , did you get anywhere with this? Have we helped enough? I'll close this issue for now; if you need more help please ask on the google group (link is in the readme).