Maybe we should back up a bit and ask a very basic game design question;
What do we WANT a weapon called a "Torpedo" to be and what qualities do we WANT it to have?
This would be my answer:
Torpedo should be a bigger, heavier, more destructive weapon than a missile.
It should be harder to defend against and certainly not easier to defend against than missiles.
Its cost should scale with its increased abilities with regard to that destructiveness and durability.
HG seems to agree when on HG31="Torpedoes are treated in every way like missiles, although they tend to be a lot more powerful."
also, and this may seem odd but still important to me:
It should have some resemblance in its use and place in game-warfare to the use of real-world naval torpedoes in real warfare.
Lastly, there should be dramatic tension as a torpedo closes in on targets a v. long or distant range.
In trying to use the rules canon we have:
A standard Torpedo costs 2.4 times the cost of a missile.
It halves the effect PD defense vs. missiles which is only allowed once per salvo.
Launch rates of missiles vs torpedoes come out to be
Barbette=5 vs 1 (presumably, rof is not explicit)
Small Bay=12 vs 3 = missile salvo 4 times effective vs. Torpedo
Med Bay=24 vs 6 = missile salvo 4 times effective vs. Torpedo
Large Bay=120 vs 30 = missile salvo 4 times effective vs. Torpedo
Damage (standard) is 4D vs 6D
So after analyzing all of this, here is my house rule suggestion (until Mg agrees with me), "Due to more ECCM Hardware packed into their larger chassis, Torpedoes are much more difficult to defeat with EW. In order to defeat a torpedo or salvo of torpedoes, you must accumulate 4 points of successful effect for each torpedo defeated.
For example, a barbette launches a torpedo in turn 1 and another in turn 2, then a third in turn 3. The sensor op attempts EW in turn 1 on the first one and gets an effect of 3, the first is still alive into turn 2. Then the sense op gets an effect of 2, this kills the first torpedo, and puts 1 point of effect on the second. 2nd torpedo is still inbound. 3rd turn, 3rd torpedo launches.
2 sensor operators, one on the bridge and one at an additional sensor station attempt to defeat a salvo of 3 inbound torpedoes. They make their rolls and each succeeds with an effect 5 totalling 10. This destroys 2 of the 3 torpedoes leaving 2 more points of effect on the 3 before it will be defeated... better hope they are at Long+ range if they want to reattempt.
This HR achieves all the design intentions I would have and I think what the RAW might prefer. They had some good rules but seemed to forget about EW and how the lower launch rate of torpedoes would make them particularly prone to it.