The 12-18 inch goldilocks zone is merely a yardstick. I had asked Mas Ayoob his opinion on this very type of ammunition. His response regarding ballistic gelatin was this:
"Good luck, Buck.
Whether the formula for ballistic gelatin was 20% or 10%, there was always the issue that ballistic gel is a homogeneous substance and the human body is a heterogeneous substance in which the human-like swine muscle tissue Dr. Martin Fackler's gelatin protocol was developed to duplicate did not give the same resistance as skin, bone, cartitlege, solid abdominal viscera, etc.
The early 147 grain subsonic Winchester OSM worked great in gelatin, but had "good news and bad news" performance in actual shootings around the country, which led to the development of both the .40 S&W cartridge and today's much more effective high-tech 147 grain 9mm bullets.
The reason the "stopping power debate" seems to be eternal is that it's simply a multi-dimensional issue with so many variables that I for one don't think it can ever be truly quantified in a "test setting." What was the toxicology screen on the man who took the bullets? How much of an adrenaline high was he on? (I have yet to meet a forensic pathologist or toxicologist who can show me a way to measure internally-generated epinephrine, post-mortem.) And, like alcohol, epinephrine affects different people in different ways, which cannot be conclusively analyzed from autopsy. Much of "stopping power speed" is determined by what is going on in the mind and the body of the attacker, neither of which can be conclusively quantified after the shooting is over. There is no study that quantifies exactly which organs were hit by which bullets at what point in the gunfight, let alone differentiating whether the "heart shot" clipped the edge of the pericardium or entered at the right atrium as opposed to the left ventricle (yes, there seems to be a difference).
For decades now, I've recommended selecting loads that work well both in gelatin AND in street performance quantified after numerous actual, investigated shootings. THEN, work on what REALLY seems to win gunfights: tactics, ability to swiftly (and if necessary, continuously) hit the parts of the body you need to shut down while firing under adverse circumstances, and an understanding of deadly force law that will allow you to deliver those hits without hesitation and not fire until you are sure of that."