Mesh region topography to be contoured

In[]:=
Show
3D Mesh Region
,BoxRatios->{Automatic,Automatic,200}
Out[]=
​

This works as expected
​i.e. Contours are rendered only within the specified polygon

In[]:=
Show​​ListContourPlot​​MeshCoordinates
3D Mesh Region
,​​RegionFunctionFunction{x,y,z},RegionMemberPolygon
Number of points: 6
Embedding dimension: 2
,{x,y}​​,​​Graphics​​​​EdgeForm[{LightGray,Thickness@Medium}],​​FaceForm[None],​​Polygon
Number of points: 217
Embedding dimension: 2
,​​EdgeForm[{Red,Thick}],​​Polygon
Number of points: 6
Embedding dimension: 2
​​​​​​
Out[]=

This doesn’t seem to work
​i.e. the contours are not contained within the specified polygon

In[]:=
Show​​ListContourPlot​​MeshCoordinates
3D Mesh Region
,​​RegionFunctionFunction{x,y,z},RegionMemberPolygon
Number of points: 217
Embedding dimension: 2
,{x,y}​​,​​Graphics​​​​EdgeForm[{Red,Thick}],​​FaceForm[None],​​Polygon
Number of points: 217
Embedding dimension: 2
​​​​​​
Out[]=