subtitles over the picture / below the picture is independant from subtitles on overlay surface.
you can adjust the vertical position of the subtitles with shift+up / shift+down (= default shortcuts)
alternatively you can right-click on the video, select subtitles->subtitles properties->custom position and place the sample wherever you want your subtitles to appear [or even use auto-position]
note: of course I am assuming your subtitles are really displayed by bsplayer, not by a 3rd-party utility such as vobsub, divxg400...
