This is a good discussion. I had just read a book not more than 2 months ago about the US war under the pacific.
The book touched ont he contactor problem too, but I can't remember exactly what it was. I want to say that the force of a "dead on" impact was "too much" and broke the firing pin before it could detonate, but that shooting at an angle decreased the impact, allowed the firing pin to detonate, and tanker ships started going boom.
That case you referred to, again iirc, was where a US Sub skipper snuck into a harbor and unloaded 4 torpedos at a stationary cargo ship from extremely short range. All four missed the target, however, the sub skipper noted that they exploded when the hit the shore. After that, iirc, the Bureau of Ordanance fired these torps at a carge net, and noted that the holes in teh cargo net were a lot deeper than the run depth setting.