The estimated original gravity in my recipie is not being updated when i add top up water to the preboil wort. Since this is a fixed batch size (5 gallons post boil) I confirmed that the est preboil volume is the same with and without the kettle top up. As a result, an increase in top up means a decrease in sparge (which i confirmed is happening in the recipie). I would think that by replacing sparge water with pure water, the OG should decrease. Am i incorrect in my assumptions?