Fl4k Fadeaway and Headhunter skill synergy

Fl4k’s Headhunter skill has obvious synergy with Fadeaway particularly when augmented by Guerrillas In The Mist.

However, Headhunter does not trigger on crits WHILE Fadeaway is active.

Occasionally, it appears Fadeaway’s cool down is reduced while in use, but after cloak ends the cool down is reset to original duration.

How are these two skills intended to interact with each other?