Logical submodel not appearing from Excel import

So I have a large custom metadata repository to import, and using Excel as the bridge seems the most comprehensive way.

But I'm having a difficult time getting Logical submodels to appear.  

First I created a sample model directly in ER/Studio, added logical submodels, and exported to Excel.

In the output I can see that submodels are defined using the "Subject Area" column.  

But when I import even that output directly generated from ER/Studio, the submodels do not appear, and all the entities are lumped under the Main Model.

What options do I have?