That depends - how is going to be opened? Context sensitive help calls from within the app using the CSH API? Or just calling the main .html page and having it open up in somebody's browser?
If your just opening the html file from a link within your site, then you could code the link to open in a new window at full size. This is not done through RH, but instead on the site where its linking to your webhelp index.html page. Its relatively simple, and you can customise things like viewable buttons, scroll bars etc etc.
have a look here: