no Scientific method really
what you can try is turning the hotspot off on your phone whilst watching the traffic, and see it drop
I just looked at my setup - I am receiving 88 traffic reports, there is a large gaggle over Husbands Bosworth, which I definitely cannot see Air-2-Air.
If you look on the traffic page, there will be a G in the last position of the Mode column, this indicates supplied via the GRID, if you are detecting directly - this will not be present
BTW, there is a slight bug-ette in the system at the moment
You are only sent traffic reports from iGRID IF you are emitting your own position
So for instance if you have set the "Aircraft Transmit Speed" to greater than zero - you will not receive iGRID reports until you are moving, a simple workaround for now is to set the "Aircraft Transmit Speed" to ZERO
This is fixed in an internal build, and will be released shortly