Swept polygon along center and a guide curve to control the size.

I try to get a surface made of a reducing polygon along a a guide curve but I get strange result.

What I would like is a polygon at each section along the vertical of the surface.

I can't find a way to do except by creating necessary control sketches and a loft between them. That would be good for simple straight lines as a guide but not for more complex one.

SolidworksSurfacing