The advice for beginners is to keep your cost values low.
For advanced pathing anything "works". For efficiency you should set your heuristicWeight to at least the minimum tile weight. The default heruristic of 1.2 is assuming roads 1, plains 2. But heuristic 6, road 5, plain 10, swamp 50, is just as efficient and returns the same path. The low values problem is because PathFinder caps the heuristic at 9 so heuristic 24, road 20, plain 40, swamp 200, should be just as efficient but it costs more.