Martin,
I have had the same experience with SPOT. Flew 3 hours yesterday
with about half the fixes 10 minutes apart and the other half 20
minutes. On other flights, and while hiking, I have had 30+ minute
time gaps. I wonder if the service is just oversubscribed and the
reliability has nothing to do with antenna placement. Thanks for
contacting SPOT and sharing their response with us.
Just one more piece of technology that we should not rely too
heavily upon. Better than nothing I suppose, but not quite what is
advertised.

Dean