Combining Surfaces For Revit

I am trying to create a divided surface from two Revit surfaces to create a sort of eggshell dome:

I rotate it and no matter how I join them, whether as a solid or surface, once exported to Revit it splits again yet remains a single mass:

If I import the two faces back into Dynamo it gives the same ID to both of them:

Hi @Jay

Could you please drop rvt file here. If you’re not able to drop then use google drive, box, one drive or similar file sharing service.

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RVT file here: