Quote BEagle: "I'm intrigued to know why the FMC computed Vapp is evidently too low?"
The FMC takes it's speeds from the information input in the Init 2 page from the loadsheet, or from the fuel prediction page if the engines are running. Loadsheets are based on notional weights, and even in Asia where I fly, those are a bit behind the times. The FMC computes the Gross Weight from the fuel quantity and your V App is calcualted from the FMC figures. However, Green Dot, VLS, V Alpha Max and V Alpha Prot are calculated from the FAC which calcualtes the Gross Weight from angle of attack and IRS data. The FAC always thinks you are heavier in the A320 series and this is particularly pronounced in the 321. Today I flew one where the FAC weight was 3.6 tonnes more than the FMC weight, and this value is not unusual.
I always increase the V app manully by 1 knot per tonne with a minimum of 3 knots. I find this works well.
And the 'below 100' conundrum'. Easily manageable in a 320, not so in a 321. The 321's throttle response (V2500) is sadly lacking. The best policy is to set manual thrust before you get to 100' in gusty conditions IMHO.