For what is worth, my las tips/tutorial video shows a torpedo launch from an Alfa's baffles, homed on passive.
Alfa reacted to it when it was around 2000 yards behind. Didn't make a difference but I was surprised to see it picked up from that far. At any rate the transient of the launch and the transit of the torpedo up to that point caused no reaction whatsoever - the AI obviously only picked it up once the torpedo was really close.
Even then, it shouldn't have picked it up that far away down his baffles XD. But I hope it's a good instance the devs can take to narrow down any possible issue and fix it
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Torpedo was fired at 26:26