why is "flatten 3D area Features" option ticked/greyed out in 'create elevational grid dialogue box'

Blooper

I'm creating a terrain mesh from a Lidar generated contour map but in the options list the 'flatten 3D area features' option is ticked and greyed out which leads to a very crystalized looking terrain map, is there a way to untick this to smooth the terrain out?

Blooper

I've found this page about scripts which seems to show a way to code that feature on or off but I've no idea how to run a script in Global mapper, would anyone be able to give a pointer?

https://www.bluemarblegeo.com/knowledgebase/global-mapper/cmd/GENERATE_ELEV_GRID.htm

"GRID_FLATTEN_AREAS - specifies that area features with elevation values should be flattened to the elevation of the area features. Use GRID_FLATTEN_AREAS=NO to disable this."