How to tweak azw3 files to trigger the enhanced typesetting feature?

Hello,

First of all, please excuse my weak English.

I am a big fan of the "enhanced typesetting" feature on Kindle.

Since this feature seems automatically enabled for KFX files, I follow with great interest the progress on KFX file generation with the Calibre plugin discussed in this thread: http://www.mobileread.com/forums/sho...d.php?t=272407.
Sadly, at this time, the generated files do not show book cover on the Kindle device.

On the other hand, when manually downloading books having enhanced typesetting enabled from my Amazon account, I get an azw3 file (KF8 format if I have correctly understood) which can be imported in Calibre (with DRM removal plugin) and then transferred on my Kindle device. These files have the same typography features as the KFX I get by downloading directly the book on my Kindle via WiFi.

I came to the conclusion that enhanced typesetting can be enabled in AZW3 files. Am I wrong?

So my question is basically: do someone know how to enable this settings in a AZW3 file? I could not find such information on the forum...
Perhaps things are much more complex... Please enlight me! :chinscratch:
Thanks in advance!