@ETOPS, there is an RTCA spec (DO-317B ) that says that only traffic with SIL and SDA equal or greater than 1 should be displayed.
SkyEcho2 is technically capable of SDA=1 but due to the way CAP1391 is written, SDA is set to 0 at the moment.
It will also depends if the RAF ticked the box for the option to have ADS-B in