Magnetic force acting on a surface with known Magnetic Flux Density

I have two different cylinder permanent magnets placed one above the other along the Z-axis. If the average magnetic flux density B for each surface is known is it possible to use the formula

to calculate the force acting on one of the magnets? I am integrating Bz over the faces of magnets and obtaining an average value for each magnet. If I input such value in the previous formula I do not seem to obtain coherent values with my experimental setup.

What am I doing wrong? Is there a simpler analytical solution for surfaces for which magnetic flux density is known?

Thank you