F100 has a collector tank which is from wing root to about 1.5m outwards. it is allways kept full. after HEL-CDG during winter estimated fuel temp was minus 5 to minus 10 degrees. refuelling with "warm" fuel was done as well via this tank but experience showed with fuel pumps off allmost no mixing took place as warm fuel went up and spilled to outer tanks via stringers.
in worst case this resulted in melting up of ice initially but when fuel pumps were switched on just before engine start as required by SOPs resulting mixing temperature could cool down upper side of wing below freezing again resulting in new ice build up if there was rain.
leaving fuel pumps on during transit stops helped as with this procedure temp of upper wing skin could only rise with outside temp above freezing but fleet manager didn`t like me not following SOP here and controlling fuel temp above freezing could make us both happy...