If you kill a tank who is oneshot, sometimes you won't get spotted, if only tank which is within the range to spot you is the one you killed.
Tested this in training room, and the result was that if the enemy dies within about 0,165 seconds of when you shoot, that tank will not spot you. It seems to not be exactly 0,165s with every tank/shell, but the results were consistently between 0,165 - 0,172 seconds. Camo value of shooter seemed to not have an effect.
This implies that for every shell velocity, there's a certain distance within which you can kill an enemy without getting spott