From just some basic physics and basic detection theory it seems like SA-15s and SA-13s should be detectable from farther away than what I'm experiencing in operation longbow (the 104th's server mission).
RF falls off at 1/R^2 1-way, 1/R^4 2-way. EW receivers get the benefit of 1/R^2 for signal strength at the receiver. There are other factors, which could be modeled, I'm trying to keep this basic.
1) How does DCS model radar transmissions & RWR receivers?
2) Is this a current issue with the harrier only?
3) Are the RED SAMS in Op. Longbow setup to turn on only when players are within a certain range?