I've just set up WordPress 4.8.2 on Ubuntu 16.04, and configured it for Multisite using sub-domains.
I can browse to wordpress.mycompany.com/wp-admin and things work fine.
If I select Sites -> Add New Site, I am aksed for the site address and it is always xxx.wordpress.mycompany.com however I do not want 3 levels of sub-domains. I'd rather have Site1.mycompany.com and Site2.mycompany.com. Is this possible, and if so how do I achieve that? Documentation I've seen on the internet always seems to assume 4 3 levels of sub-domains.