Time to cut a bit off the seatpost?
Not much help but I would be in the same predicament as you with an Anthem, although my legs are a little longer. 18in definitely too long and little standover, but think I would get away without cutting the post, but 16 would be on the small side.
I really don’t want to until I’m absolutely sure and unless I try the small frame I will never know and it will always bug me, like I can’t get it out of my head already! I think I’ll have to put my seat post in it from my old bike and at least tray with that, but to be honest I’m never gonna be satisfied until I at least know what the small is like!