Ok so the 3% thing might be referring to the actual rate of interception, as in, only 3% of incoming fire is intercepted. I haven't looked at the source that Iamassu is quoting. The numbers I usually see is that interceptors work 50 to 75% of the time.

I believe this is mostly correct. The 3% is the overall rate of interception so this would include missiles launched where no attempt to intercept was made. When referring to the success rate per interceptor, 50 to 75% is probably still too high. Professor Postal also claims that for each missile, 2 or 3 interceptors are needed to even have a chance at interception.

I unfortunately can't find his work in text format anywhere, but he's been making the rounds on the alt-media platforms. The one I saw was his recent interview with Glenn Diesen.