If you find that you have lost the 'state', take a second to put the tangerine back on top and behind your head again. Keep doing this everytime you loose state, it takes a fraction of a second to do, but yields wonders!! In time, it will stick ... for good!
Just a thought. I know that when I worry about losing the tangerine then I constantly lose it.
(I think that Paul mentions on one of the tapes that after you have established the tangerine you don't have to worry about it anymore because part of your attention will naturally stay focused on that point.) Now I don't worry about it and it works out much better for me.