Hi,
The moisture parameter in the grain is for informational use and does not impact the water volume calculation.
The challenge here is that water absorption is not necessarily a function of moisture content (for all possible fermentables). A sweet potato does not absorb water the same way that crushed barley grain does for example. I would need a pretty complex model to handle all of these cases.
So internally the program applies the global grain absorption (though there is a separate global for BIAB due to the bag compression when draining).
Brad