I'm not relying on it absolutely, there's plenty of liquid honey already in my 14x12s, even if very little ended up in the supers! And if the Ivy is as disappointing as most things this year, they'll be getting some syrup. (The late swarm is already, but not on the OP's scale.)
And there's Ambrosia if need be for late syrup feeding.
Hives in the garden can be closely monitored ...
One job for this week is to get some tidy lugs and attach them to the floors, so that I can weigh the hives one side at a time. At about 35kg currently, I can just about lift them, but I discovered that I can't weigh them at the same time!
I'm just surprised that the OP has been feeding on this scale, this early. Though, as I pointed out, its microclimate that counts, and I'm surprised hers would be so severe as to need to feed that sort of quantity, this early. Were the hives empty, or are they now pretty full?
A single brood National needs to be rammed pretty full with winter stores. A 14x12 will hold rather more than the 20kg ration advised. Feeding until they stop taking it, with a 14x12, this early, seems extremely ... generous!
Another aspect would be the bees themselves.
I know very little of Italian bees, other than they reputedly take the provision of feed as a trigger for additional brooding. Thus, I gather, they can take enormous amounts of food, without laying down much stores, rather raising brood.
Could that be a factor here?