Two things. One is how advanced the system is (software, internal hardware). Another is how elaborate and powerful it is: how many receivers and active emitters, how good are their FoVs - how much real estate is given to the system, both inside and outside; how much power; and so on.This is based on opinion that Chinese does not does not have analogues to SPECTRA. Given Chinese leaps and bounds in semiconductor field, it no surprise if J10C itself has build in EW suite. After all CAC did have delegations touring Dassault when Rafale was still a prototype. While Russians still relies on wingtip jamming pods, Sino flankers have incorporated its EW suite into the plane itself.
PLA fighters (like, say, americans, israelis and most of the world) don't carry all that much base(J-20 is exception of course, it's embedded with arrays all round). When in need of EW, they carry larger (more comprehensive) pods under the wing.
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