Hi Peter,
using (C:ITrafficInfo:Filter) xml custom variables and setting filter as TRAFFIC_FILTER_AIRCRAFT or'ed with TRAFFIC_FILTER_ON_GROUND (9) it happens that ground traffic is rendered but not detected by C:ITrafficInfo
in FSX/P3D the filter works correctly.
Odd that if you set the filter as TRAFFIC_FILTER_ON_GROUND or'ed with TRAFFIC_FILTER_SLEEPING (40) object are detected only if they have an altitude more than 10 feet on ground, thus if you set a boat (as an aircraft) into the sea this is not detected until you move it on land where the ground is some feet above MSL.
ciao
/Mario