This setting varies from zero to one and has no dimensions. When set at zero it is inactive and when set at one, the upper profile is fully set, as described below.

The Upper Profile: Top setting defines the shape of the surfaces where the backbore runs up into the throat. It creates a radius between the Backbore Nodal Point and the bottom of the throat radius. The nodal point is slid up and down the backbore using the Backbore Depth setting and in and out by means of the Backbore Width setting. In the diagram below, (a) shows the standard throat/backbore configuration while (b) shows the form when the Backbore Width setting is moved in the positive direction and the backbore is opened out. View (c) in this diagram shows the situation when the Backbore Nodal Point is slid down the mouthpiece backbore using the Backbore Height setting. The blue arrows shows the start and finish points of the trajectory of the nodal point and the red dots show its position. View (d) shows the shape of the backbore when the Upper Profile Top setting slider has been moved in the positive direction to its fullest extent. Under this condition, a radius is formed between the backbore and the throat at position e, indicated by the purple arrow.