As it has been a while since you posted this, I hope you've found an answer to your header question.
Headers aren't included with Tabcmd PDF download.
Headers Missing when Exporting to PDF Using tabcmd
However i'm not sure how we apply the height/width options with Tableau server client - i don't see a width option in the API reference guide, maybe it's undocumented, might be worth checking if the option can be applied there?
Hope this helps!
I am facing the same issue. And it doesn't happen in case of dashboards only sheets when published as views. Please suggest a possible solution to this.