Thanks guys for your input.
What you have said is correct and makes sense.
What my question was , instead of reducing to actual weight prevailing , e.g. at 43C read speeds and EPR , someone reads speeds on 43C ( thats were actual weight is ) but instead of taking EPR also from 43C column of which we all do , he takes somewhere halfway between 43C and where it gives max thrust ( actual temp column).
They say this procedure gives early lift-off ( good for rough runways ) .
I have not seen this in performance books , so im asking is it true that it gives early lift-off ?
Is it a common procedure anywhere ?
Zenj