Partial mash home brewer here. Since I'm not doing a full boil (only about 4 gallons), is there even a point in taking a pre-boil gravity if I'm going to end up adding top off water post boil? I'd like to be able to calculate my efficiency. Will the top off water (and lack of extract) make it pointless? I know the top off water is added after the boil, but I'm just making sure.