Orthobro here, the most I can really tell you is basic history about Chalcedon and that Coptic services are quite long. I've been told that they can go on for 5 or 6 hours at a time.
When flags were on we had a Copt or two that would occasionally pop up, but it wasn't anything near common. You're more than likely going to be relying on them seeing this to get the kind of detailed insight you're probably looking for, but I wouldn't bet on them being around.
As far as I know, we've never had an Ethiopian post here, but they're a whole different box of chocolates from the Copts. I'd actually be interested myself to hear someone from that church talk about their traditions.