custom header image and it's path

hello, 🙂

I’m trying to use the custom header image functionality (<?php header_image(); ?>)on my custom theme with a wp network with folders and using domain mapping.

the problem is … at the network-site domain the path/url of the header looks like this:

http://mainsite.com/network-site-folder/files/logo.jpg

when I understand it should be:

http://network-site.com/files/logo.jpg

as for example looks (work correctly) the path/url of a image I insert in any post.

???

—
on the side… and not related at all with the main question:
I tried a “system” of my own to load all the logos, and the idea was to use a php inside the files folder to load the logo from another -not_to_show- location where all the logos would be. and the plan was good but when I call the php network-site.com/files/logo.php it dosnt run… but instead show me the code like if was html.
is not possible to run phps in there?
any idea about this?

thank you!!