I've used the EBC calculator and put in a recipe which includes 3.91 kg of MOpale 2 row,.23 k of German munich light,.25 kg of UK crystal light and .22 kg of German pale wheat. Brew length is 23 litres. If I enter all these into the calculator I get an EBC of 13.88. However if I enter each ingredient separately then add them up I get a total EBC of 18.93. Why is this please?