E.g., we can only access /data/data/com.termux/* https://developer.android.com/training/data-storage/app-specific
So as Termux sets HOME=/data/data/com.termux/files/home we can use its $HOME as a keystone to access the rest of its tree. (However other apps' internal directory structure will probably differ, so we can't just assume $HOME/../bin, $HOME/../usr/tmp .) Anyway, we have avoided hardwiring full paths by instead grabbing on to items from the environment. So the user could first do $ ssh machine env to see what he could grab on to, to do something similar in his .emacs.
