[TYPO3] levelfield with slide

[Loek Hilgersom]

I'm trying to use the TS slide option for a custom field I created in the page 
properties, but I don't get it to work:

     subparts.topImage = IMAGE
     subparts.topImage.file {
         import.data = levelfield: -1,tx_pacheader_headerimage,slide
         import = uploads/tx_pacheader/
         import.listNum = 0
     }

Do I misunderstand how levelfield should work?

It works alright with the media field and levelmedia:

         import.data = levelmedia: -1,"slide"
         import = uploads/media/
         import.listNum = 0

Any ideas on how I can get this to work for fields other than media, title or 
uid? (those 3 have their own level... option)

Thanks,
Loek