A320 Tankering & anti icing

[che ci dō che ci dō!]

Good day everybody,

let's say one has to do a two stage refuelling with an A320 and at destination the OAT is above zero but there's rain and/or visible moisture. If the flight time is long enough the remaining fuel in the wing tanks would be well below zero and if he FOB is above a certain value the upper chamber of the wing comes into contact with cold fuel thus leading to clear ice formation.
Does any one know which is the max FOB at destination in order not to have the upper chamber into contact with cold fuel thus avoiding de/anti icing?

Thanks!