I just cracked a test container with only the first 512 bytes, your doing something wrong if you can't get it to work.
To make things really easy, make a copy of the container, open it in your hex viewer (you should just dd instead but seeing as you like using your hex viewer) and delete everything after the 512th byte and then point hashcat at it.
To make things really easy, make a copy of the container, open it in your hex viewer (you should just dd instead but seeing as you like using your hex viewer) and delete everything after the 512th byte and then point hashcat at it.