The designer sets the max width, its radius is then mathmatically stepped down to create the proportioned incut and tapering angles. Max width defines the Ratio.
The maximum change in angle of the top edge. This is set by the intended application angle. A top edge with a 45 degree apex utilizes a proportional width and length and defines its taper angles.
The change in planes. A curve is not flat and climbers will take advantage, selecting the correct ratio for the difficulty is important to creating usability. Wall taper is often part of an incut and must be correctly selected for the ergonomic value as well.
THE TOP EDGE
The top edge is a change in angle from the body to a new plane, the griping area. This curve or edge is made proportionate to the ratio set by max body width.
The Incut is determined by the pad width and the intended application angle set by the designer. This area of grip must work in unison with the Apex.
THE BOTTOM LINE
The human hand is proportional to the golden ratio, so the same ratio is used to design all the holds. The individual attributes are simply scaled up or down to match the intended hold size.