Box Sign API - Renaming signed file

I am creating a sign request for a file in box called MyCompany_NDA.pdf. 

When I send the payload I include a 'name' parameter under source files in the JSON body of the request, but each time the signed file gets posted it just goes into the folder as MyCompany_NDA(1).pdf etc. 

I could create a folder called SigningCompany under my NDA folder, then put the signed docs in there, but ideally I would like to keep all the signed docs in one folder, and just have them renamed to SigningCompany_NDA.pdf