Sweep2 with maintain height is not maintaining height on a small object

[Tom_P]

there is also some similar topics -

C Scroll surfaces

Hi John- the way your original curves are set up, one hits the planar area ‘hard’ with a sharp corner, and one dips slightly behind then comes back to the planar area. I cleaned up the latter but left the hard intersection as this seemed to be part of the design. I would make that intersection planar as well, myself, and avoid that slight kink at where the scroll meets the flat. -Pascal

How to create this shape?

I need to model the ceiling panel in the attached image. I have two areas I’m struggling with here. First, how does one create the converging arc shapes that are increasingly wider as they spread? Secondly, how does one then have those shapes extruded with an increasing thickness as it gets to the middle of the circular shape? Thank you.[51%20PM]

but there was a newer one - i cant find - i tried:
acanthus ? helix ? spiral ? scroll ?