This turned out to be the fix! Both urls are now working as expected showing the current url as HTTP_HOST.
I've removed the host: $host aswel, but the fix by Sebahat seems to have fixed it before already.
Awesome help, thank you both!
We discovered a weird setting where php's $_SERVER['HTTP_HOST'] is always set to the domain alias's target. Previously, expected and on a copy of the same subscription, its supposed to display the current url.
This is necessary because of Prestashop Multistore.
main url: url.nl
Alias: URL.com...