There is no automatic support for POM with tri planar mapping yet. You could do it but it would require making 2 new nodes that swizzle the camera vector into the correct spaces.
For the Z (top down) projection no swizzle is necessary
For the XZ you need to swizzle it so that the Z from the original camera vector becomes the X, in addition to flipping the sign based on if the X is positive or negative.
For the YZ you would need to swizzle it so that the Z from the original camera vector because the Y, in addition to flipping the sign based on if the Y is positive or negative.
So as you can see POM needs to be performed 3 separate times and modifications to each. One day I will get around to making an example out of it but I haven’t had time yet.
You can make POM work with a single world aligned XY coordinates. Simply set the “Use World Coords” to true on the input bool.