Reference 11 has been added after Equation 10, to point the reader to where to find information about phi limits was first discussed. Repeating this information here would complicate the paper. The lines Phi = 2^(1/3) and 4^(1/3) in Figure 1d have now been explained.
How the authors derive the range [0.9, 101/3] for the so called “reduced surface” index? In Figure 1d, Lines 21/3 and 41/3 have some particular meanings, or are plotted mainly to ease the figure comprehension? Could the authors add some indications about the derivation of these upper limits?