Well, you have asked an excellent question.
We already have radars with 400+ km ranges. The Arudhra radar from LRDE has a 400 km instrumented range with a 300 km detection range for a 2sqm target. Now do the maths.
But here's what interesting. The Americans ie the US Navy has a system of systems or rather an architecture which is known as NIFC-CA. National Integrated Fire control - counter air.
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Here in any airborne sensor which is generally a E-2D Hawkeye or a F-35C picks up and tracks a hostile aircraft or a missile beyond the radar range and / or under the radar horizon of the SPY-1 radars of the Alreigh Burke destroyers or Ticonderoga class of cruisers which would then fire it's SM-6 missile in order to intercept the threat. This leverages the superior coverage of the E-2D along with the long range of the SM series of missiles. The E-2D uses the TTNT network and act as nodes while other acs like the F/A-18 E/F interacts with the E-2 through Link 16.
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The IAF may use a similar system. I believe something like this is already in the works which will leverage the Netra and connect it with the IACCS.
Besides all our ground based radars and Sam systems be it E Shorads like Spyder SR or Akash mk1 to MRSAM and the long ranged S-400 are all plugged into the IACCS. So whatever one radar detects and tracks irrespective of the geographical area, the requisite feed is available to the rest of the shooters and sensors plugged into the network.