It doesn't have to be, defender reveals everything and attacker chooses best strategy.

1. The defender could use both electronic and physical decoys, use air and sea mobile platforms that are always in motion and are difficult to track.

2. The defender can fire at decoys, to convince the attacker the decoys work when they don't.

3. The defender could mix in cheap decoy interceptor missiles that miss so the attacker concludes defenders need 10 missiles to intercept when the real number if 3 and the attacker thinks the defenders are running low on interceptors, when in fact the defenders have held most of their interceptors in reserve.

4. Defender can pretend that expensive systems have been destroyed so that attacker adapts their strategy. For instance, if your defense hinges on a small number of extremely expensive fixed X-band radars and the attacker targets them. Allow some of them to be appear to be destroyed when in fact, you have disassembled them and moved them somewhere else to use later in the war.

I see no evidence anyone is doing any of this today, I'm not making any sort of claims about deception operations in the current conflict.

Many historical wars have been won by deception.

Sun Tzu taught us: When you are weak, appear strong. When you are strong, appear weak.