The reference is actually in many manuals, but not directly described.
Think in the quote in the 737 FCTM reads: "airplane attitude at a normal touchdown speed (VREF to VREF - 5 knots)"
In all Performance Inflight charts for LDR it refers to 305m (1000') air distance in accordance with FAA rules, so JAA operators or airfields need to be adjusted according to JAA markers set at 400m, add an additional 95m in other words unless TDZ is promulgated non-standard JAA markings (for example LDY).
Furthermore the charts add a Vref additive which is applied to find the LDR.