Recently I bought my first pinball machine - a MM in a visually good condition. During setup of the playfield slope to the recommended 6.5 degrees (measured directly on the playfield), I noticed that the lower playfield has a different slope than the upper playfield. When I set the lower playfield to 6.5, the upper (beginning from the middle of the playfield) only has 5.5 degrees. I am measuring with a small digital inclinometer mounted on a 40cm long leveler. I double checked the result with a smartphone app, which roughly shows the same results.
Is it normal, that the upper playfield somehow "overhangs" the middle hooks and has a different slope that the lower playfield (which sits straight on the hooks and the support brackets)? What could be the cause of the different slopes and how could I fix that?