How to set up composer autoloader?

Question

Composer

Now I have it written like this

{
  "autoload": {
    "psr-4": {
      "Module\\": [
        "app/modules",
        "system/modules"
      ]
    },
  }
}

And the classes are available at this path root:app\modules\ModuleName\SomeClass.php
How can I force the composer to look not at the root of the ModuleName module, but at the \src folder in it, but so that the namespace would be preserved Module\ModuleName ?