The value of Proximity Gap Factor is an estimate, it may not be exactly satisfied in every gap. When using mapped Face Meshing controls or sweeping, interval assignment may change the number of divisions (elements or cells) in a gap.

For thin regions, to control the aspect ratio of the cells in the gap, you can use Proximity Gap Factor less than 1. For example, if you want to refine the surface mesh to allow elements with an aspect ratio of 4 in the gap, you can use a Proximity Gap Factor of 0.25

In cases involving Patch Conforming tetra meshing and Swept meshing, the proximity sizing drives the surface mesh size distribution as follows. The value of Proximity Gap Factor is applicable to both 3D proximity (the number of 3D elements/cells between two faces in a body) and 2D proximity (the number of 2D elements/cells between two edges on a face), and the global Growth Rate value is automatically taken into account in the gap. However, the 3D proximity sizing affects only the surface mesh in the gap, and assumes the volume mesh will use the global settings. Hence, if you define local mesh sizing on a body and specify local Element Size or local Growth Rate settings that differ drastically from the global sizing settings (or if inflation is specified), the final number of cells across a 3D gap may deviate from the specified Proximity Gap Factor value.

When Method is set to Automatic, the proximity calculation in swept bodies may result in an under-refined mesh. You can use inflation layers or a scoped fixed size at such locations to produce a sufficient number of elements/cells.