Spraying Barley (Dry planted 57 days since emergence)

Yesterday I was applying 10kg ha of Potassium Sulphate together with 250mls of Tilt, barley was planted dry with a full profile (1meter of wet soil) but about 15 cm of dry soil on top, this crop has had 155mm of rain since emergence. It is looking very strong although time will tell.
I would estimate there was approximately 180/200mm of PAW (plant available water) in the soil at the time of emergence, add to this the 155mm of "in crop" rainfall of 155mm =335mm less 110mm to allow for evaporation (French/Schultz method) and we have 225mm available for grain fill.
The general range of WUE of wheat and Barley (water use efficiency) is 10kg per mm of grain to 20kg per mm of grain.(can be a bit higher or lower)
So with 225mm available for grain fill at 10kg per mm = 2.25 t ha (2250kg per ha) poor WUE
or at 20kg per mm it would yield 4.5 t ha (4500kg per ha) which would be a good WUE.
Only time will tell.