Maybe what else is needed is how much does each shot take away? I take it the shots count the same, they just hit more often the closer the target is.
This might fall into more of a suggestion category, but what would be really helpful is if the health and shield statuses were marked at the quarters (4 bars), since that's how the AI breaks them down. If the classes have differing total shield and health "points," maybe the health and shield status should be differing lengths? It would visually demonstrate the strengths of the differing classes.