I run at 4.5 ltrs/kg, place the bag in a bucket to drain and poor 8 ltrs of hot water over it (to get my volumes and extra sugar) and get 70% in the fermenter. That scenario is 9 kg of grain in a 50 ltr keggle, making 31 ltrs of high gravity wort, once diluted 40 ltrs of 1.050
Key to good BIAB...