For me this about the balance of evidence in its historical context so probability rather certainty.

The base of sarcophagus is at the level where the area of the triangular cross-sections of the pyramid is divided into 2 sections with the same area, and each half is equal to the area of a semi-circle with the circle's diameter equal to the height of the pyramid, as calculated from the pi approximation 22/7.

Petrie's model of the sarcophagus was that the exterior perimeter was a model of the circumference of a circle. He used Smyth's maxima for the external length and breadth, but on reference to Smyth's survey Smyth had picked these dimensions out as anomalies on adjacent sides at the bottom of the sarcophagus insofar as he repeated his measurements, so it was actually only a semi-circle in Petrie's model and at the very level of the pyramid denoting a semi-circle, because the other two sides at the base of the sarcophagus had rather shorter lengths which meant the full circuit of the sarcophagus was the same.

Petrie regarded other anomalies as poor workmanship, but then based his theory on two anomalous dimensions, although he did concede that some other objective was probably in view in the mind of the designer.

Mark