Bob,
You might try completing the partial 'loop' that you
have now. Probably no large difference in performance
but who knows? If there is any particular band of
frequencies you listen to you might try an antenna resonant
for that. Probably the one thing that will make the most
difference is a change to vertical polarization, a vertical
of some kind. There are a lot of "ought to"s and "shoulds"
but experimenting is one good way to find out...
'Doc