When the ‘modelfit’ or ‘trend’ style is used with the Cloud chart, a mesh surface is drawn through the 3D scatter. The default is to draw the mesh with one line at each X and each Y major tickmark.

ch.Set 'Density' 2

This parameter may be set to any value (1 is the default) to add extra lines in between the ticks. Values less than 1 thin out the mesh as you would expect.

This example shows a trend surface drawn with a mesh density of 2.

See also ...
ch.Cloud – 3D scatter plots