Question: why are my exposed grayscale color parameters are capped at 0.8114

Ive noticed recently that when i expose a uniform color grayscale node as a parameter in designer, the value of the parameter appears capped when using the material in substance painter. As far as i can tell setting the value to the "maximum" of 0.8114 is equivalent to 1, or pure white, but this is obviously not ideal. Is this a bug or something i can fix?  screenshot below for reference, i am unable to move the Brush Roughness slider any higher