How exactly does proximity fuse in Vega missiles work?
Is it somehow linked with GSN?

I know it is activated when GSN antenna movement is faster than 30 degrees per second (if I remember correctly) and what then?
Proximity fuse will start to receive reflected RPC signal, but how is the exact warhead ignition time calculated? Since the target can be elsewhere and its radar reflectivity is also undefined, the system can not rely on received signal strength only (it can vary a lot). It can evaluate received signal change with time (the first or the second derivation) but I think it is not sufficient also. When you have fast incoming target, the warhead must be ignited well before missile gets to close vicinity of the target. The opposing situation is when the missile is "hunting" fast receding target - in this case warhead detonation must be significantly delayed contrary to the first scenario described.

This leads me to fact that proximity fuse must be closely linked to GSN, but how to tell when it is the right moment for detonation?