Some thoughts, perhaps ...
(a) a particular aircraft will be certificated with whatever approach speed to 50ft. Come significantly below that and come to grief and you have some awkward questions to answer .. because you weren't supposed to be there.
(b) STOL is a military animal and involves takeoff and landing operation at speeds rather less than the normal civil certification requirements. The additional risk associated with a reduced speed pad is an accepted operational consideration. So, as a general observation, when we talk about "STOL" in respect of civil aircraft, we are talking through our hats somewhat and really are referring to operations at the minimum speeds. Just what minimum speeds .. well that can vary a bit according to the story teller.
(c) it is common practice, especially on light aircraft to approach at speeds a little above the AFM/POH book value(s), I guess to add a bit for inexperience, mum and the kids, and whatever else. Providing that the excess speed isn't so great as to cause undue float etc., and you have plenty of runway, no real problem. However, the legit minimum speed remains whatever the POH says it should it be .. go slower and prang, and you need a good story.
(d) we all are well aware that, in the good old days of yore, folks were a bit gamer and used approach speeds somewhat less than the book value .. just don't get caught out.
(e) 1.3 by 25 = 37.5, what am I missing?
What most folk miss when they try to do this sort of sum while not knowing what is required. The quoted end figures, presumably IAS, have whatever PEC involved. You need to convert the starting figure to CAS, do the sum, and then convert the answer back to IAS. Then you should get the answer sought. The report quoted in the earlier post doesn't have enough information to know just what they are talking about specifically.
Down in the stall region weeds, PEC can become a bit significant .. we all know that the little Cessnas can hang on the prop with nothing on the clock bar the maker's name .. but the "speed" indicated has little to do with reality, I'm afraid.