You are indeed right, I apologize for this misunderstanding. Configuring NewRowPosition will add a placeholder to the bottom of RadGridView, however, it will be like a placeholder and not like empty new row. Once you fill data in the first newly added row (after clicking on "Click to insert new row ...") though and press the Tab key, then a new empty row will be added from now on.
As it turns out, there is not another option to suggest. I apologize for this inconvenience.