The upper halves are cut on an index of 2, or half way between 64 ( or 0 ) and 4. The angle of the upper halves is 40.58 degrees. This is how the upper halves are normally cut.
The girdle thickness is equal at the mains and upper half junctions.
A 'hearts and arrows' simulation of the above stone:
A FirescopeTM simulation of the above stone:
Simulating the American Gem Society's ASET ( Angular Spectrum Evaluation Tool ), here's a color-coded map of how the diamond utilizes light:
White is leakage ( defined as an area that does not return light ), green is from 0 to 45 degrees from the horizon, red is from 45 to 75 degrees, and blue is 75 to 90 degrees.
The upper girdle facets draw light from the red area ( 45 to 75 degrees ).
Lastly, a brightness simulation:
