Missiles don’t always follow a straight course, I don’t know about the AMRAAM, but the Phoenix would climb to a very high altitude early in it’s flight, and dive down later. So perhaps if it was seen as it got close, the smoke trail wouldn’t be very helpful in finding the source.
OTOH, I would think the missile itself would be immediately visible to radar, which would also be a strong indicator of where the firing aircraft is – another good reason for a stealth bomber not to fire one.
Of course so much of my military “knowledge” comes out of Tom Clancy novels that I’m not always sure what is truth and what is someone’s imagination.
I think you need to go back to Giulia Douhet (Command of the Air) to see where it originated.
And you also need to consider the experience of The Great War. The bomber did get through.
Look at the raids on London. (There were raids on Paris as well but they aren’t as well documented). First of all the Zeppelins came and eventually a few were bought down.
So, the Germans switched to Gothas (twin engined) and they were successful until the British pulled Sopwith Camels (needed at the front) back home. So they switched to night time raids and very few were lost.
Then- and this was the crunch- the germans used the Giants. They were roughly the size of a Super Fortress. These aircraft, flown from Belgium caused havoc and panic out of all comparison to their numbers. How many were bought down by anti aircraft fire, fighters, or barrage balloons? Not one. That is right- none.
At the end of the war the British were astounded that only 22 Giants had ever been built. The resources wasted trying to combat them had been enormous. Hence their mindset (initially at least) that the bomber would (did) get through.