The thickness of the base of the front feet is thinner/shorter than that that of the back feet, giving you the illusion that they aren't level.
It was not my point : I was not comparing the front-side feet with the back-side feet, but the back-side feet between them... After @kvetcha's reply and looking carefully the pictures I sent before from MOFI's web page I understand now this is normal that the motor-side foot is more compressed than the tonearm-side foot... I am attaching another picture from web which also shows the difference (+/- 1mm) between two back-side feet.