ECON cruise, LR cruise...
Join Date: Apr 2002
Location: MIRSI hold - give or take...
Age: 52
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....but LDR from your AFM is given from 50' (apart from certain steep approach perf charts or corrected for runway upslope in some fashion) - and that's your target THR crossing height. So LDA is measured from the threshold.
Your deceleration will often begin well before touching down, as you typically will have some Vref+ - corrections applied for wind or similar. These need to be washed off to cross threshold at 50' and at Vref, with further deceleration from 50' till touchdown.
So - the beyond g/s-figure is not used for any practical application on the line (ie excluding test-pilot- and runway design-stuff).