postfix multidomain myhostname configuration

I have two IP address running on Postfix and each IP has own domain. In short i want to isolate domain so outside folks think it is running on own IP and fully isolated even PTR also

But in postfix it not handling myhostname option IP specifically. it always use default value set in mail.cf file

I have tried to set -o myhostname=abc but it still using mail.cf value. Because of it my IP got block in SPAM list

How do i set IP specific myhostname so HELO banner looks good