Edzup reported a while back in the bug reports forum that entitybox does not follow sprite orientation correctly. If that is the case (I have not investigated it myself) you may be better of using a quad mesh (or as Edzup suggests try changing the spriteviewmode). Test this assumption by placing the sprite directly in front of the camera (when the camera is at world origin and aligned to the world axis). Presumably the box will then work as it should because the sprite will not have changed its original orientation.
http://www.blitzbasic.co.nz/Community/posts.php?topic=35178
http://www.blitzbasic.co.nz/Community/posts.php?topic=35178