andre... i totally agree with u as far as i understand what u say. there is only one focus plane for everything - all the rest is illusion of physical and physiological limits.
the dof marks on the lenses are very practical, but those are just a "logical" approximations.
that what i have said - that u talk about the magnification.
what i was talking about is not the magnification element of optics and its appearance on the negative surface, but about the angle of view.
angle of view is the other important element to control the perspective. wide angle lenses are have "dynamic" apearance not only because the front/back relation, but mainly because of the angle of view which gives u the sense as if u turn your head around (especially pronounced in some kinds of object arangement in the space). at the centre (the radius of the centre is upon your critical approach to this metter) the perspective is about the same for all focal lenghts - means, if u point your camera directly forward, with all focals it will look the same - "direct forward perspective" (with defferance of magnification/distance etc).
but as u go aside of the negative surface u will find differances:
the long lense for will remain almost the same (direct forward) on the all negative surface,
while the short lense will record the sides in defferent perspective - as if looking from the side, or if the camera is vertical it will be from up and dawn. the normal lense is somewhere in between. the wider u go the more pronounced is the effect of the angle of view and the longer u go the more directly u look at the whole scene. of course everything has its practical and creative use. in practice, this knowledge means nothing much, without applaying it to the arrangement of the space and what u want from this space and things in it.