Using NavMesh.Raycast to detect if AI should jump over a gap

In my side scroller game I want my AI characters to freely navigate between platforms, which often leads to jumping. To tell if AI should jump or not, I'm using NavMesh.RayCast to tell if there is gap between navmeshes that is connected with offmesh links. Now, this works well in most cases, but completely fails with navmeshes taht overlap in Y axis(there is walkable platform above another walkable platform). The problem is apparent in pictures below:

and a code snippet:

  private bool TestJump(Vector3 currentPosition, Vector3 targetPosition)
     {
         NavMeshHit hit;
         bool potentialJump = NavMesh.Raycast(currentPosition, targetPosition + new Vector3(0,0.4f,0), out hit, NavMesh.AllAreas);
         if(hit.hit)
         {
             Debug.DrawLine(currentPosition, targetPosition, Color.yellow, 0); 
         }
         else
         {
             Debug.DrawLine(hit.position, currentPosition, Color.red, 0);
         }
         return hit.hit;
     }
     private void PlotPath()
     {
         if (_pathCache != null)
         {
             var a = _pathCache.ToList();
             for (int i = 0; i < a.Count()- 1; i++)
             {
                 var v1 = a[i] ;
                 var v2 = a[i+1] ;
                 float t;
                 if (!TestJump(v1, v2))
                 {
                     Debug.DrawLine(v1, v2, Color.green, 0);
                 }
 
             }
         }
     }

Am I missing something here, or navmesh raycasting is completely useless when it comes to multi level navmeshes?

Thanks.