Somewhere you will probably have a statment where the right column module output is processed.
<?php if ($this->countModules( 'right' )
&& JRequest::getCmd('task') != 'edit' ) : ?>
<jdoc:include type="modules" name="right" style="rounded" />
<?php endif; ?>
You can see with the addition of && JRequest::getCmd(‘task’) != ‘edit’ it will also check to see if an editor is running. If there is, the right column will not be shown and there will be more space for the editor (assuming the template has fluid center column)