Get Retail Channel Name using Reference Group

Hi, 

I'm creating a form with a grid to display All Sales Order Headers like in SalesTableListPage form. 

In my grid, I want to display retail channel name using Reference Group instead of display method because I want the field to be available for sorting and filtering. 

So I simply added RetailChannelTable field into the grid. However, unlike WorkerSalesTaker field, RetailChannelTable reference group does not contain the string control. 

I though it's because AutoIdentification field group in RetailChannelTable doesn't contain any field. But I cannot add any field into this field group.

So I extends  RetailChannelTable and added a new field group ChannelName containing the name method. 

Then I change the Replacement Field Group to this ChannelName Field Group.

Even so, since I cannot add a string control inside the Reference Group, the field won't appear in the form. Note that I already build and rebuild the project.

Why is it like this?  How can I add the string control inside the Reference Group?

Thank You.