The differing water-to-grain ratios are most likely due to different amounts of grain in the recipes. For BIAB, BeerSmith computes the amount of mash water needed to end up with your target volume after grain absorption, boiloff and other losses are taken into account. The amount of mash water needed will be almost the same for all recipes, with grain absorption being the major difference. If the amount of water stays fixed, then your water/grain ratio will change as your amount of grain changes. For example with my default recipe if I use 8 lbs of grain it tells me to add 7.53 gallons of water, for a ratio of 3.766 qts/lb. If I change the grain quantity to 10 lbs BeerSmith tells me to add 7.68 gallons of water, which is a ratio of 3.071 qts/lb. The water increased by 0.15 gallons to account for the increased grain absorption, but the grain weight increased by a larger percentage, so the water/grain ratio went down.

--GF