Okay, well let's put an armor roll at six. If I roll a five, I only get to target something within one inch. That's fine. However if I roll a two, suddenly I've quadrupled my range and can choose from a slew of targets within 4".
Oh wait, hold on I think I see the miscommunication: here I'm thinking that you resolve a whole new attack against the next target, but you still use the original damage roll so that actually balances it back out (somewhat).
Still, I could see someone targeting a heavy tank or something and abusing that pretty har. Say something like 18 damage rolled vs. 31 armor: That leaves 17 damage to be dealt to any target within 13 inches, which is more than enough to slay a hero. I'd recommend adding another use roll in there if I didn't immediately forsee that as an extra step that slows the game down even further.