The flare height ranges from 20-40ft depends on weight, or you can fixed the flare height at let say 30ft but change the rate of flare due to weight difference to achieve the same result.

That would make sense, given that extra weight results in extra inertia.

 

A big airliner like the 777 would usually be landing at a pretty standard weight though most of the time. And I note that the autoland pays no attention to weight when flaring, same height for thrust reduction and same height for flare, every time. So I'm not sure the minor change in mass and inertia has a significant effect in regard to the 777.

Thank you all!

I recommend you to use VREF30 + 5 knot (except with heavy gust). The 5 knot additive is bled off during the flare; I mean, VREF30+5 during approach to be at VREF30+0 at touchdown. Initiate the flare when the main gear is about 20 feet above the runway, reducing thrust to idle and increasing the pitch about 2-3 degrees. And do not trim during the flare, because increasing the possibility of a tail strike.