Have you ever needed to create a volume or solid in Revit and wanted to keep the plan area the same (conserved) when one or both plan dimensions changed? You have two options to do this and it will be up to you do decide which one to use based on if you want 1 pull handle or 2…..
The following image summarizes this process.
Why does Revit remove the second pull handle when the area is made into an input parameter? I have no idea and when I discovered this I didn’t spend anytime asking “why” I just created an other option (option 2)… and when I wanted two pull handles I would edit the family and change the area. I never let Revit’s limitations slow me down.
Try it for yourself and good luck!