stalling and guessing
Bis47,
.......I think for whatever reason the stall did not occur at 170 ft . Free fall from that height calculates a far higher vertical speed than the 2000 ft per minute indicated by the damage.(Edit - I assumed stall to occur from an existing descent rate of about 1100 fpm)
......My rough calculations indicate a stall about half a second before impact, below 50 ft (I got a nominal17ft agl) with the nose just beginning to fall, such that there was no visible tailstrike mark.
....I guess if it was in a mushed but still steady descent at 2000fpm there would have been more tail down