Today, I will try something new. As I find Technical Solutions posted in the Autodesk website, that related to Autodesk Civil 3D, that I believe are notable I will provide the link to them.
This is the first. TS1056340 describes why "Minimize Flat Areas" will not affect surfaces created by LandXML.
Why? because "Minimize Flat Areas" is intended to be used on surfaces made from contour data.
Click on the hyperlink above or the title of this post to see the full solution.