8k export not matching 4k export

My 8k export is not matching visually (except for resolution of course) the 4k export - I am masking between two materials in folders with an image alpha - and the export matches if I just export either material by themselves - but any masking element -procedural or image makes it so they are not identical as if the greys are weaker in 8k  -I have an nvidia quadro M6000 24gb card - windows 10 - and running Adobe Substance 3D Painter Version 7.2.3 build 1197  -thx