Hi again, I have access to my computer now. Little wonder you had trouble figuring this out yourself, as it was quite a bit more complicated than anticipated. In the Gameplay Grids function it is very straightforward to identify which edges are diagonal and which are straight, but at a later point this is more tricky, as the Edge Array does not distinguish between various forms of edges. There are many ways to determine this, however, so it is definately doable, but takes a bit more work than just doubling the edge costs set in the graphs. You just need to alter one macro, though, which is the Get Edge Cost from Z difference macro. Here is how to alter it so that it sets the edge costs of all straight edges to 2 and all diagonal edges to 3:
Here is the original for comparison:
Since this modification alters the inputs of the macro you will also need to connect the index of the parent tile instead of the Z height of the parent tile every place the macro is used. It is used three times in Add Viewport Terrain To Arrays. You can easily find all three by right clicking the macro in the MyBlueprint tile and selecting Find References.
This seems to do the trick. Hope that helps!