It really doesn't matter where you put anything, as long as you only upload it once (even if it falls under multiple categories). The key is to label the file on your computer very clearly (so like "pattricerafferty_personal_statement_on_relationship" or whatever).
If you really want to find the right category, go to thr bottom of the upload page and beneath all tge recommended categories there should be a button that says "add documents" or something. Click that and you'll get two drop down menus. You can find any possible category that way.