Unable to create form element - Cylindrical Adaptive Family

[ames.hardt]

This is more of a curiosity than a problem - does anyone know why this particular form won't generate? It's a single face cylindrical form in an adaptive component template. If the cylindrical face is made up of two lines and two arcs, it won't create the form unless the curve is deep enough (screenshots to show what I mean.) I can make the form if I use splines instead of arcs, but then the face isn't cylindrical which is important for me to maintain.

I know there are other ways to make this form, but I'm surprised Revit isn't able to patch and create such a simple cylindrical face unless it has a deep curvature.

For some background, this is actually a family that would be generated and used by a Revit plugin, but this behavior persists even when the family is made manually so it's not an API problem. I'd like to create these types of forms as adaptive families to stay consistent with the rest of the app, especially since this is only one simple example of what the app could (ideally) generate.

Does anyone know any solutions or workarounds for this? I've attached the family to show the difference 

[ToanDN]

You only need two curves to create the form, not the straight lines.

[ames.hardt]

I'm aware, hence why I specified this as a curiosity - lofting won't work for other conditions that my app needs to support. If I can't patch a simple shallow cylindrical face, it's almost certainly not going to handle others. I may need to use DirectShape instead of adaptive families for my curved conditions.

[ToanDN]

What other conditions?  Here is the form created as a true partial cylinder.

[ames.hardt]

Nice. How were you able to patch it?

[ToanDN]

Same way as I said earlier: only select the two arcs to create form, do not select the longitude lines.