PEI_3721, Thank you for the clarification.
I DID say "Simple pilot answer" and, having looked at your impressive CV, I am sure you are aware that we use approximations in day to day operations, e.g. descent point = HATx3 +7 +/_ wind allowance, timings in visual circuit etc and then adjust as the flight progresses.
I would say that a safety margin is, by definition an 'about' arbitrary figure.
I've a feeling my 'about 60%' is x1.67. E.g.
AFAIK structural safety margins in aircraft may be from 1.5 to 3.0 but in ships, up to 6.0.
Re the B737 temp correction; at SL 45C that would add 300ft which is covered by the 60%.
the resulting distances involve many assumptions, predominantly variation in flight path control, speed, and some environmental aspects, but not in combination
Hence my closing comment which event I have witnessed twice; once as a passenger in an Aztec (almost went into a ditch) and once as FO in a Viscount which burst all main tyres. (Yes, I did point out the problem to the PiC but he continued - more work needed on FO assertiveness
)