However your Sollecito's reference measurement is 102-103 mm.
That would probably work anyway for a good overlay of the contour.
However the contour of the print should be visible, so it should be overlayed to the print for a better assessment.
I think Rinaldi's measurements on the prints are correct, but I consider the photo is definitley a less precise source of information on what regards proportion and measurement, also because of the intrinsic optical properties of photography, which always produces a slight deformation, albeit not perceived by the eye, unless there are some very sophisticate and very professional conter-measurements, special equipments, etc. Only a centimetred grid over the stain would produce a good retference.
The properties of deformation / shrinking of the bathmat as a soft material are also potentially influent on proportions and scale error.
The assessment of the correct scale on two images like thesre is not a banal operation. In fact it has to follow a morphologic assessment: to understand what are the points of reference and the degree of rotation of one in respect to the other, before confronting the scales.