you can only have h1 -> h2 -> h3, i.e. you need a h1 before you can get a h2, before you can get a h3. If you want different looks, the way to go is to alter the stylesheet.
1. Copy ./design/standard/templates/content/datatype/view/ezxmltags/header.tpl
to your design folder e.g ./design/mydesign/templates/content/datatype/view/ezxmltags/header.tpl
2. Edit ./design/mydesign/templates/content/datatype/view/ezxmltags/header.tpl replacing the hX tags with what you require.