I now realized that all asset paths (js, css, images, layouts) are relative to source directory.
So, all you need to do is to set:
config[:source] = 'ofir/files'
and REMOVE all other directory configs you posted, as default relative paths are correct. Until you change config for source directory, Middleman assume it is
source directory, which in your case isn't the case.
If this still doesn't work, you need to post directory structure of your Middleman directory (that is: one where there is
config.rb file; this is the same one where you run middleman server from), so that I can see what does it look like.