@jeff_strater wrote:
If I understand your question, this should work exactly as you expect it.
Agreed, it probably "should" work, but it is still not a good idea to design this in a single 3D sketch.
When I see a user doing it here on the forum, it is almost exclusively done by users who have no experience in a modern parametric CAD system.
In any parametric CAD system I know, 3D sketches are reserved for specific purposes, e.g. piping, wiring, cables, etc., or perhaps to feed a frame generator.
It is definitely a better practice to create only those curves as 3D curves that really need to curve through space and not be constrained to a plane. All other curves should be designed in their own sketches, constrained flat to a construction plane. If Fusion 360 had a tool to planarize a spline similar to Autodesk Alias my recommendation might be differnt, but it doesn't.