After customising the fields and setting up the form through the 'tab customisation.'

I then go into web forms to set up the form ready to extract the code for my website.

The only problem is that I've created two customised 'File Upload Fields' 1. For uploading a resume. 2. For uploading a cover letter. The cover letter field does not display in the webforms dropdown menu when setting up the form. 

Why is this?