If your ECM was still on, that would be the problem: Imagine a RADAR like a night vision sensor, looking into a dark room. It can see the planes going around up to a certain range and also their range. Now how the SPJ (self protection jammer) like your sorbtsiya is like a huge flashlight you shine into the RADAR. The RADAR just sees a big bloom of light in your direction, but can not see the range. And now thing you have your ECM on at 500km away from the enemy RADAR: He will still be able to see and lock you but can still not determine your range.
If you did not have your jammer on, please provide a track file, it always helps understand the problem. Please do not just make post, saying DCS is doing somerthing incorrectly, maybe it is your own fault.