iBooks vs Audible app

iOS 10.3.1 on iPhone 6 plus.

Audible.app 2.22 (405)

iTunes 12.6 on Mac Sierra (10.12.4).

When I import an .m4a file into iTunes on my Mac, set its type to 'Audiobook' and mark it for synchronization with my iPhone, it appears in both Apple iBooks (latest version) on my iPhone and the Audible app. (But not iBooks on my iMac desktop.)

Is that normal/expected, please; can it be sent to either one or the other?

Thanks so much in advance!