Optimisation for stealth against bistatic and multistatic radar systems is a different problem from the monostatic case. The important thing is the split between the position of the transmitter and receiver. In the monostatic (transmitter and receiver in the same place) case, you need to optimise to reduce radar energy reflected back in the direction of the transmitter.
When the receiver and transmitter are split, this problem gets harder, because you need to optimise to reduce radar energy transmitted back in the direction that recievers are likely to be (or don't reflect any, but that's a different problem). This becomes even harder in multi-receiver systems, and even harder in multi-receiver-multi-transmitter systems. As computation power and communication bandwidth becomes cheaper, lower power, smaller and easier to hide, many of the assumptions used during the development of the current generation (and past generations) of stealth aircraft are becoming invalid.
Passive location systems, either secondary radars or systems using 'transmitters of opportunity' also reduce the effectiveness of anti-radiation weapons significantly.
