How hard was the impact? Did you yell? I only ask because my SO just had an accidental contact car-to-car where both parties backed out of parking spaces convergently. Our bike rack which was folded took the brunt of it in a springy motion but Liberty plus rack vs a Prius didn't fare as well for the Prius. The problem is the springy/rattle of the rack negated the sensation(reportedly, since I wasn't there) and didn't make it apparent to need to stop. It later came to our attention when the police came to the door.
All this to say not all contact is readily apparent over modern radios or rattling cars. In most cases though I would agree the drivers SHOULD know when overtaking and that is why I like using obnoxious lights and a little less 'inviting' posture. In the daytime I set my headlight to super strobe as well. Sometimes it makes people cringe but they stop when they do, so its effective.