Before "Extrude with Taper" After "Extrude with Taper"
Create a regular polygon (sheet body) with "Regular Polygon" command.
Select the sheet body and [Extrude with Taper].
Specify Extrusion vector in the normal direction to the face, and push button.
Keeping the reference point as is, click
The top face will never be a vertex as the scale factor is always more than 0.