My PF Core picks up all ModeC/ADSB targets perfectly well, while stationary in my city street in front of my house. Most of the traffic is on approach into a major airport at 3000ft, 3.5NM laterally displaced.
If I open up my ranges in the configuration file, I can see also departing traffic much further away and much higher.

There have been reports here on RAS from people evaluating the PF and MRX side-by-side, who have concluded that the latest PF firmwares outperform the MRX.

Do you understand what your $PFLAC,S,OWNMODEC,1 is for ? (I have mine set to 0)

3U.