I saw an older post in 2011 that was slightly pertinent to this topic, but not quite what I was looking for.
I have a new Profile Zcoaster, Flybikes Tractor Chain, and 20t Profile Spline Drive sprocket on Ares Illblend 160mm cranks.
I used to have an Ezra freecoaster hooked to the exact same drive train.
I understand that the Zcoaster is a completely different animal when it comes to hubs. I enjoyed the ability of the Ezra to immediately disengage and allow me to go directly from forward rolling to backward rolling. I have even experienced some engagement of the Zcoaster while in a disengaged forward roll (the pawls start buzzing lightly, then fully engage and throw my cranks).
I have adjusted the slack on the Zcoaster with appropraite slackrings and positions thereof. When I place it in a 33° slack adjustment, the engagement issue dissipates, but leaves me with more than desirable slack. The 20° slack setting appears optimal for me.
I'm wondering if changing to a larger sprocket (22t, 23t, etc.) will give me just enough travel difference to allow me to utilize the 20° slack option, but without the engagement problems.
I'm also considering just buying another Ezra or an Odyssey Clutch and corresponding spokes, and doing away with the Zcoaster altogether, but i'm not quite ready to give up on it just yet (especially because of the large investment I have made in it).