Copied your shader but it doesn't do same the same thing.
When moving the spread value up or down, it doesn't have any effect on map range node mask in eevee or cycles. Ambient occlusion is on.

Hi @cgwookie I haven't tried this yet, but the spread value cannot have any effect, because your Color> MixRGB > Subtract Node has a Fac of 0, which means it doesn't do anything with what comes in at the bottom socket.
If subtract node is 1, then there is a on/off effect for spread
Here is 6.5

Here is 6.6

Other than that, it has no effect