I've been following this discussion with interest, as I've never seen any information or calculations using distance from touchdown. All I get is the LDA (which may differ from the overall runway length) from the aerodrome charts and tables in the QRH (shortly to become an "app") with distances from 50' over the threshold. Factor as required.
Taking the example of LAX 24R, which by coincidence I landed a 777-300 on at MLW a week or two ago, my documentation reads:
TORA 2720m / 8925ft
LDA 2720m / 8925ft
3deg PAPI,
MEHT 77ft
Now, not having any guidance material about MEHT and its implications, I had a root around and found a UK CAA document with this explanation:
8.5 The Minimum Eye Height over Threshold (MEHT), which is notified in AIP, is a reference value, calculated with respect to the promulgated approach angle for each PAPI. It is the lowest eye height over the runway threshold at which an on-slope indication will be seen. From examination of published MEHT, it may at first sight appear that for some runways, adequate wheel clearance at the threshold is not assured for all types of aircraft likely to use those runways. However, a typical eye height achieved in practice when crossing the threshold following well established 'on slope' approach would in fact be well above the published MEHT value.
From that, I infer that the figure of 77ft for LAX 24R (or indeed 73ft for LHR 27R) does not affect the LDR, so I can carry on as normal. Phew!