The blue represents the starting profile of this recut. Even though the diamond started out deep, the crown angles were flat and as a result the diameter of the stone had to be reduced to raise those angles.
Even without the Table Reflection Method, very deep pavilions are easily spotted from a distance. Deep pavilions are noticeably dark due to loss of light and a very large table reflection. They are very common, because of the desire for maximum weight retention in many cutting shops. This is especially the case with lower quality goods, since these stones will not face the degree of scrutiny that finer qualities would.
In re-cutting diamonds, the general rule of thumb with deep pavilions, is to gauge finished weight by the starting diameter of the diamond. The only exceptions to this rule are if inclusion removal comes into play, or if the crown requires steeper angles or a smaller table. If that’s the case, more girdle will likely be necessary, thus reducing the diameter of the stone.