Firebase functions: set region when using reserved hosting urls

I currently have my firebase setup like this (without a config, as the reserved hosting urls load the config automatically):

var functions = firebase.functions();
    if(window.location.hostname === "localhost") {
        firebase.functions().useFunctionsEmulator('http://localhost:5001');
    }
    var db = firebase.firestore();
    var perf = firebase.performance();

But, I cannot set the region to a different place, as I want it to be in europe-west2. I've tried adding it as a parameter to the firebase.functions() without success.

This is what I have tried, according to the docs:

var functions = firebase.app().functions('europe-west2');

without success.

Is there any way that I can do this?

Thanks in advance.