Tomas Slancik

If you want to use VEX to compute the values you create an attribute first and then reference it in the parameter using Hscript or Python expression

The above mentioned Reference/Scene Data option is a shortcut that builds that expression for you without having to type it, even though arguably typing may be faster once you already know the syntax

Definitely a known limitation as the help for all MtlX or Karma ramp nodes mention only linear interpolation

I personally find MtlX standard very constraining and almost not evolving, giving me feel of being stuck 15-20 years in the past compared to modern shading solutions, especially for renderers that can't use OSL or MDL like Karma

I dont think there is a built in way to distribute sparse pyro sim, just the dense one

However if you can split your source into several chunks you can use wedging to run your sim on each of them independently using the same graph