Getting close…
My landscape sections are 504 x 504m, so needed to multiply this by 100 to get to world units. Ideally I would like to detect this from the landscape, but for now will just make this a configurable parameter in the material function which is fine.
Also neglected to take into consideration negative coordinate values that would cause the FMOD / IF sections to ignore all negative coordinate values, so added an ABS conversion before the FMOD.
Improved blueprint looks like this:
So this works fine along the origin edges, but not at the other end of the landscape… Still digging…