The element could be coarsened if its position is far enough from any geometry triangle, i.e., the distance of the SPH element to any geometry triangle should be higher than the Refinement Distance Factor times initial SPH Size (), where d is the Refinement Distance Factor and s the SPH Element Size. Therefore, if this triangle belongs to a geometry marked to be part of the refinement process or not, this distance condition should be satisfied. This is done to minimize of overlaps between walls and SPH elements and aims to avoid high instabilities, an issue caused by a possible loss of mass, see Limitations of the SPH Adaptive Sizing.

The sum of both SPH Elements refinement count values. If the sum of refinement count values is smaller than the maximum refinement count, which is equal to , where n is Refinement Level, the coarsening can happen.

Refers to the distance of the two elements to be merged. They will be merged if they are a distance between each other lower than the average of their smoothing length. In other words, two SPH elements are merged when the distance between them are lower than , where h stands for smoothing length, which is given by the product of Kernel Distance Factor times SPH Element Size.