The distance is "fixed" by design. The only way I know of to change the distance is to change the size/scale of the symbol being used or to change the overall drawing scale but then again it will still be relative to the extents of the the symbol.
ACADuser
Civil 3D 2018, Raster Design 2018
Windows 7 Enterprise
Dell Precision 5810 Workstation
Intel Xeon E5-1630 v3 @ 3.70GHz
32GB RAM, NVIDIA Quadro K2200 4 GB GDDR5
DUAL 27" Dell UltraSharp U2713HM