From a purely medical perspective, the only difference wearing the carrier on top really makes is it allows you to dump your plate carrier before someone gets overzealous with a set of trauma shears. If it can fit in the jaws of trauma shears the ER staff will try to cut it, backboard straps, anti-shock trousers, EKG wires, pacing pad wires (while the patient was being paced), all these I have personally watch fall victim to "trauma teams". Anyways, speaking as a Paramedic if it's anything serious you're going to learn the term "trauma naked" real quick, I'm not too concerned with the order I have to go in to get there and as long as I can find the velcro and quick release buckles that's how your vest is coming off. I've had to take vests off injured cops a few times, not really an issue. That said, wear the vest on top when possible because it gives me something to grab onto and drag your ass to safety if need be.