Type 1 jamming seems to be nearly a hundred times as effective as it should be.
While working on a plug, I changed around the jamming vulnerabilities of the IR and radar missile, giving them 35% in types 1 and 2, respectively. I then flew a ship with outfits giving equal jamming in both types and found there to be a massive difference. I started doing some hunting to try and fix the problem and make sure I hadn't somehow screwed up the IR missiles while tinkering.
Changing the IRs vulnerability to type 2 but with the same value confirmed that I hadn't imagined it or jinxed them somehow - their accuracy improved dramatically, even though I had equal jamming in both types. I also tried changing radar missiles from 35% type 2 vulnerability to 35% type 1 vulnerability and found that they, too, were then jammed 100% of the time.
After a while, I had my type 1 jamming set to 45% and started varying the type 1 vulnerability of the IR missiles. I would pick a value, go into the game, and shoot a standard Federation Destroyer. Its 80 missiles would give me a fairly accurate picture of how effective jamming was. I didn't get hit by any significant number of missiles until I went down to 2% vulnerability. Right now my plug has IRs at 1% vulnerability, and a significant fraction of IRs still get jammed.
During all this flying around and getting shot at, I also found that type 2 jamming seemed to work more often that it should. I spent some pirate-hunting in Scheall with radar missiles set to 35% vulnerability and me having 50% jamming. At least a dozen times, a Pirate T-head would unload its clip of 10 radar missiles at me and have all 10 of them get jammed, rather than the expected rate of (35% of 50%) * 10 = 1.75. I spent a very long time getting shot at in the name of plug-in development, so I can say with confidence that it wasn't a random number fluke, although it isn't as bad as IRs - at 35/25 vulnerability/jamming, something like 80% of the radar missiles get through.
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