Is there a setting in nix.conf?
You probably want to do this in your ssh config.
Hmm not ideal, many hosts to manage.
Actually, I think I found the answer, with Nix 2.4 at least: adding
?compress=true to the hostname seems to do the trick. I created add `?compress=true` to ssh store urls · Issue #178 · DBCDK/morph · GitHub to get this into morph.