Something else that would be interesting is attempting to bridge the two with a small wire or conductive tape. This could eliminate the act of holding the phone as a variable, and isolate it to bridging the antennas.
Unless your wire or tape behaved the the same as a human hand in terms of inductance and capacitance, I don't think there'd be much you could conclude.
Radio-frequency circuits behave very differently at the tuned frequencies than they do under direct-current.