Please reply with the analytical formula you are using for the max shear stress in the rivet.

Many analytical formulas calculate the average stress in the cross-section of the rivet. Ansys calculates element stress which changes from one side to the other. You can add Construction Geometry to your model and put a Surface at the plane between the plates. You can plot the stress in the rivet on that surface and look at the average stress.

The problem with bolt pretension is that it splits the cylinder in the middle to pull each side together to apply the load which will interfere with extracting stress on the construction surface.