If a model with mines & Sixth Sense (any level) is targeted by an attack outside their LoF, can you place a mine as an ARO? My thinking would be no, because in the reactive turn, it says you need LoF to place a mine, and Sixth Sense doesn't give you LoF, it just "Allows the user to respond with a Face to Face Roll to Attacks (and only Attacks) directed at him by an enemy outside his LoF and regardless the facing of the user.", and placing a mine doesn't result in a Face-to-Face roll. Is this understanding correct?
I don't see why not. You can respond with a Chain Rifle which isn't FtF either, so I don't see what prevents you from doing so. Could be wrong though.
I guess I wouldn't see that as "responding to the attack" more like "ignoring the attack" ? Haha... It does seem like a bit of a grey area though, yeah.
There are unfortunately some grey areas where "face to face roll" is used kind of loosely to mean "skill that could produce a FtF roll, even if it doesn't in this particular instance". So I'm not really sure if you can drop a mine or not in this situation.
Responding with a "BS Attack, <DTW>", "BS Attack, Smoke Grenade that doesn't Block LOF" or similar is contentious but broadly agreed to. This moves beyond that. Without clarification in an FAQ I'd say 'no, you can't deploy the mine'. I think the line is - as @toadchild has it - a "skill that could produce a FtF roll, even if it doesn't in this particular instance".