Brilliance is not simply a matter of adding more facets. It comes from directing light so that it enters through the crown, reflects inside the pavilion and returns to the viewer. Every gemstone material bends light by a different amount, so successful pavilion angles depend on refractive index.
When a pavilion is too shallow, light can pass through the bottom instead of returning. This creates a pale window in the centre. If it is excessively deep, areas may remain dark because the reflections do not reach the viewer efficiently.
Cutters also work with real material rather than perfect diagrams. A strong colour zone, an inclusion or the original shape of valuable rough may justify a small compromise. The goal is a coherent face-up result, not mathematical conformity for its own sake.
To assess a stone, move it slowly under soft light rather than judging one still photograph. Look for balanced flashes across the face, limited dead areas and a pattern that remains attractive as the stone tilts. Good light return feels lively, but it should also support the gem’s colour and character.