only one segment of URL leads to ProcessWire-page

[typ9]

Our client tries to reach the new ProcessWire page via reverse proxy, so he redirects client-domain.de/test/ via proxy_pass to the URL where we provide the website.
On the server, we set the domain 'client-domain.de' to the right ProcessWire webspace, and we set the httpHosts in config.php to 'client-domain.de/test'
With this configuration we manage to load the start page, but all the paths and links don't fit (stylesheets, scripts, subpages), because their URL is 'client-domain.de' without the '/test'.

Can anyone advice how to change the settings to get this working? Any help is appreciated!