Maybe I miss something but why is .bashrc or .zshrc not the correct level?
I think what @frlan is saying is that `.bashrc` and `.zshrc` are shell specific setup files and wherever possible things should be set up in a common file, but I don't know what that would be since [zsh](http://zsh.sourceforge.net/Doc/Release/Files.html#Startup_002fShutdown-Files) files all start with `z` and [bash](https://www.gnu.org/software/bash/manual/html_node/Bash-Startup-Files.html) files don't.
Also of course depends on login vs interactive vs neither.