If you manually alter the roughness and obtain different results, and if the parametric method delivers different results from the manual approach then please make sure if your parameters are defined correctly. If you can, share the screenshots of how you set up the input and output parameters.

Please follow this links to get more information : Working with Parameters and Design Points (ansys.com) and  Performing Parametric Studies (ansys.com)


If you are not able to access the link, refer to this forum discussion: How to access the ANSYS Online Help