Yeah, you are right…
what I did:
- added a domain name in my router f.e. assistant.url
- added a lease for HA on it’s IP f.e. 192.168.100.100 and gave it a name f.e. home
After that, your router should be able to resolve home.assistant.url as the reserved IP
(home.assistant.url should equal your qualified https dns name 
)