Here's a house rule I've devised that you could use on unspotted units. It came up in a conversation over at Grogheads. It's completely untested btw but might be worth a look.. You could fire on an unspotted unit but would pay a penalty where you're only using half fire power as you're firing at the hex, not the unit. If the attacker wins, the defender makes a MC with the difference being the modifier. If they pass, the unit is still unspotted and they have the option of immediately opfiring on the attacker. If they fail the MC they're automatically spotted and if they fail by 1, they immediately opfire at the attacker, if they fail by 2-3, they're shaken, if they fail by 4 or more, they take a step loss. (Those numbers are all arbitrary btw, you'd have to test it to get the correct range).