Link cost Represents the quality of the link to an active neighbor. The higher the Received Signal Strength Indication (RSSI), the better the path to the neighbor and the mesh portal. If the RSSI value is below the configured threshold, the link cost is penalized to filter marginal links. A less direct, higher quality link may be preferred over the marginal link.
The link cost is dependent on the environment and also the position of the APs. What kind of antennas are you using for the mesh links. If it is directional then there could be an issue with how they are aligned.
Node cost Indicates the amount of traffic expected to traverse the mesh node. The more traffic, the higher the node cost. When establishing a mesh link, nodes with less traffic take precedence. The node cost is dependent on the number of children a mesh node supports. It can change as the mesh network topology changes, for example if new children are added to the network or old children disconnect from the network.
I think node cost and the path cost can be optmized based on the network you are trying to design. What is the network topology for your application?
Path cost is calculated by adding the link cost plus mesh parent's path cost plus the parent's node cost. Mesh portals typically advertise a path-cost of zero, but high-throughput portals will add an offset penalty if they are connected to a 10/100mbps port that is too slow to for the high-throughput link capacity.
Mesh points use the configured algorithm to compute a “path cost,” for each potential uplink and select the one with the lowest value as the optimal path to the mesh portal.