I don't think the 200km is slant, rather it might be ballistic, from point A in the ground to point B in the ground.
The HHQ-9 report is Chinese but I can't say if its authoritative or from Internet speculator.
I would assume both effective and slant range would be half of ballistic range. Also, the missile is only as good as far as the radar is effective, which means the target has to be LOS with the radar and at sufficiently close range to get an accurate track and speed of the target. The radar also has to illuminate the target for missile guidance.
As range goes further, PRF (pulse repetitive frequency, Pulse per second) lengthens proportionately. Electronic advancements can't fudge physics by the way; pulse length is directly determined by distance and the speed of light. As PRF and PPS drops, so does the tracking accuracy and the measurement of speed, ambiguity starts entering, and so does loss in signal gain and increased vulnerability to countermeasures.