I’m not running a ZCO but I’ve standardized on 1.5” mounts for everything. On chassis rifles it seems to be a sweet spot. I started with a 1.18” on my MPA and moved to 1.5” at the end.
I have both mouth heights and the zco527. The 1.18" works well if you dont have a handgaurd. For chassis systems like AI or cadex of even the whiskey 3 with aluminum closed forend you'll need the 1.5" especially if you have flip caps.