Andy would be able to answer this in more detail but the EW numbers are basically the ability to deal with the EW value of SAM's......if your aircraft has a lessor EW value than the missile being fired at it then the missile has the advantage...if the aircraft EW is higher than the SAM that's being fired at it then the aircraft has a better chance of fending off the missile.
Right now based on all the info I've seen I've given the Chengdu J-20 an EW of 10
agreed it **appears** to be aimed at LR strikes of support assets and for that it only needs to be stealthy heading right at you. It has 8 HP's and that's why it has 8 " things that go boom"......IGNORE THE COST SHOWN.....I don't run the cost calc until just before the patch ships