I've read a few dozen posts and, as quoted above, the holy post. Still, if it's me being thick, let me know.
My question: I could swear I did actually have to change my nginx site config and was getting errors until I enabled port 80 (which has been off for months). Also, there's a ton of posts about having WAN port 80 map to 81, which maps to 80 inside the container. Why would all that be needed, if validation doesn't get done through my server on port 80? I'm sure there's a answer and that it's 90% likely to be that I'm an idiot, 9% likely something has changed, and 1% (shock/horror) the "no nginx changes/ separate web server" is misleading, easily misunderstood, or even incorrect.
In any case, feel free to ignore me--I'm up and running with this awesome image. Thank you all for a great thing and all your support and information here.