Heigh as input image alpha?

I am accustomed to have height saved to color image alpha  of png files.   Comes from photogrammetry editing process that way. The height is never lost .      Now  I want to make sbsar that would  feed that image to Painter   with a switch that would  treat alpha as  regular alpha or sending it to height channel  while  using rgb as alpha.    

How  should I name outputs in designer  ? Specifically one  being regular alpha .     Does Painter have some specific rules for alpha naming?