without modifying CSS, inputs panels can be inserted only in the top of the form or in one or more panels.
Go to Edit - Source and insert
<row><panel></panel></row> between the first row and the second row. After this you will be able to drag'n'drop text input field to this new panel - it will be between the top and the 2 lower panels.
This is a good work around. Create an empty panel through the xml/html and then drag the input filter to this panel, visually it still stays between the two rows of panel, upvoted...