Sorry this is a bit late:
The weight loss in attack is mostly water; in attack the body is forced to use up its store of glycogen in the muscles and liver, which is the first place it normally turns to for energy in the absence of carbs. Glycogen is closely combined with water, so as the glycogen is used up, the water is liberated.
Once the glycogen is gone, the attack phase is over, and in cruise the body is forced to use stored fat to create energy - hence the second, slower but more permanent weight loss in cruise.
BUT - if your BMI is already very low you won't have as much retained water as someone with a very high BMI; big sponges hold more water than smaller sponges.
So, someone with your BMI simply won't see the huge losses in attack that others may see, and there is no point is extending attack beyond three days - the sponge is dry, and it's time to go on to cruise and start burning fat.