The lens-object distance for a given magnification depends only on the focal length d = f(1+1/m).
For 5x macro, this Mitakon lens should have d = 85mm (1+1/5) = 102mm, and the Canon d = 65mm (1+1/5) = 78mm.
Mind you, these measurements should be taken from the front nodal point, not from the front of the lens, but that maintains the same correlation as the working distance. Longer lens means longer working distance.