The options in the Generation and Overlap Mode panel control the relative position among the fibers in the pile (or with the objects of the structure currently in memory).

Fibers may touch (but not overlap) when Prohibit Fiber Overlap is selected. Fibers may not touch when Use Isolation Distance is selected, and a positive value is entered. Then, the gaps between fibers have at least this preset voxel distance. The choice of Use Isolation Distance may lead to long computation times when using a high resolution in big structures.