The surface is the flat surface used in the contact pair. Create a Coordinate System and select that flat surface. Name that coordinate system CP. The Coordinate System will be created at the centroid of that flat surface. After it is created, change the definition of the origin from Geometry to Global Coordinates. Now you can reposition the CP coordinate system origin by typing in numbers to move it to a location at the center of pressure of the contact. When you request a moment reaction, change the default and select the CP coordinate system. The moment should come out close to zero.
Follow the rest of 's advice to drive it to be as small as you care to. When you request the Force reaction and choose the CP coordinate system, the arrow should look like what you want to see.