I'm pretty new to this but it looks to me from your code that you just haven't set up the WA upload to also create thumbnails.
All you have to do is this; On stage 2 of 2 when setting up the uploader, the first option is the File Settings. Beneath it is sais +/-. Click on the +. If you click inside the list of [Filename]'s in the box you can edit them as you did before by selecting them. Remember that the new Filename is set to create your thumbnails by default.
I'm pretty sure that's you buddy.