Content Expert question: Mobi or KF8 download

Dear Kindle experts,

I've been wrecking my brain over this for hours now:
Is there a way to make absolutely sure, that a Paperwhite 3 or equivalent Kindle will definitely download a personal document in AZW3 from a Mobi that has been converted as a “dual-mobi” in Calibre.
I have been experimenting with the same book and all sorts of different configurations (PDOC EBOK tag, embedded fonts) and so far have found no reliable procedure to make sure that only azw3 downloads. The only thing I have noticed: Once the PW3 has “chosen” a particular format, there is no way to change that.
I want this format for a number of reasons and do not mind that book covers are missing. However, I have found not set of settings that makes sure that azw3 files are reliably downloaded.