Lighting "Edge Normals" issue

I’m attempting to steal the “edge normals” technique from Backbone : Backbone - Working with 2D Pixel Art in a 3D World | Unreal Indie Dev Days 2019 | Unreal Engine - YouTube

I’ve got materials set up, normals baked from Sprite Illuminator (generates edge normals) - but I’m finding that lights are not reacting like the Backbone demo.

I’ve tested with directional/point/rect lights - but get odd shadowing glitches across the surface, and the light does not effect the edges equally. For example, if the light Y pos creates a rim-light effect on one side and I move the light to the other at the same Y pos, no rim light effect is visible. I have to move the light to a different Y. Even then, the effect is not clean, with no ability to create a rim light without the main light bleeding a lot onto the surface.

Confusingly, if I use NormalFromHeightmap node to convert a height map I get the expected effect (except one edge is always a bit janky due to not being able to get the UV offset right)

I expect about -0 responses to this rambling noodlefest, but and tips would be greatly appreciated.

Can you take a look at yours shader