Hi Lara,
So this: """"""How would you place at beginning the cutting objects in order to avoid the distance differents at the lofts? Ideas?"""""""

From this post and image: """""""http://moi3d.com/forum/index.php?webtag=MOI&msg=10096.37""""""""""

Is answered this way... Notice you spoke about how the result is identical, "Under and reversed" in that area...

That is because your chamfers are going in 2 different directions, so the up and down side of the "slant" is opposite.

To get the symmetry in the place you want, with equal proportions, your "cutting objects" should be a "Mirror" of each other (Not a copy). This reverses the "slants", so they are opposite, and produce results that "face and duplicate" each other...

"Copying" the cutting objects will have the "reversed direction chamfers" produce "reversed symmetries"

Let me know if this is too hard to follow.