I just got my SPOT in time for the Seniors, and I also opted for the
parachute harness mounting option. In my well-reclined position, and
with the glider straight and level, the unit is oriented almost
horizontally.

Mark Hawkins, the creator of the very cool spot mapping app being
tested right now at the Seniors, has told me that my SPOT tracking
messages are getting through about 90-95% of the time for the 7 days I
have flown so far here in sunny Florida.

BTW, just to add credence to Steve & Darryl's comments about patch
antenna performance, I also make (or made) my living designing and
analyzing the performance of antennas of all types. A patch antenna
such as the type on the SPOT system has a pretty broad pattern with
it's main lobe oriented perpendicular to the plane of the patch (i.e,
straight out the front of the unit), and is typically mounted such
that the rest of the electronics blocks the back lobe, causing the
degradation noted by Steve in his gazebo testing.

The good news, so to speak, is that a SPOT-sized patch antenna at
these frequencies will have such a broad pattern that the degradation
in performance between perpendicular and 45 degrees off probably isn't
all that bad;-).

Regards,

Frank (TA)