747 pilots are aware of the small ground clearance on lift off. At that moment, clearance is minimal, and can be as low as an incredible 18''. Therefore, correct rotation rates must be used to prevent too high an attitude before lift off, and in the engine failure case, very slightly slower rotation to a reduced attitude target. The later -400 had a printer that would print out after take-off unsatisfactory rotation technique! One dreaded hearing the printer spring into life!
Whilst the loadsheet would give the tail trim setting for take-off to give a standard rotation 'feel' to the elevator, one had to be prepared for the position of the C of G being fore or aft and changing the amount of force needed to rotate. It could make a significant difference and either make rotation too heavy, or too light and causing over rotation. Remember at the same time you may have a strong crosswind to contend with!