*Hello Damien*

In the case you mention. Have you tried using =require= for that?
I have always used it successfully in such situations. I.e. importing
units/modules in paths relative to the current directory of the
module(s).

#+begin_src scheme
(require "my-scheme-file.scm")
(require "some-dir/scheme-file1.scm")
(require "another-dir/scheme-file2.scm")
#+end_src

*Greetings.*