The IPs allowed to access WebAdmin are set in 'Management >> WebAdmin Settings' on the 'Access Control' tab. It's not clear from your description that you need a static route. Is the 172.16.5.x subnet connected directly to the Astaro? Is the Astaro the default gateway for that subnet? What is at 172.16.5.1?
The IPs allowed to access WebAdmin are set in 'Management >> WebAdmin Settings' on the 'Access Control' tab. It's not clear from your description that you need a static route. Is the 172.16.5.x subnet connected directly to the Astaro? Is the Astaro the default gateway for that subnet? What is at 172.16.5.1?