Smoked stout recipe questions

I'm looking to make my first foray into mashing with a smoked stout partial mash. I'm looking to mimic BIAB style, with what is essentially a prolonged steeping in a bag and some sparging of the bag once it's drained. My goal is to make a smoky dry stout. I'd love any tips or feedback. I know that the water volume of my mash is high but I don't see how I can do BIAB style with only the recommend 4.5 quarts or so.

Infusion mash at 150F in 2 gal water for 60 min:
1lb 2 row
1lb smoked malt
8oz black malt
6oz roasted barley
8oz flaked barley

Drain, then "sparge" with 1 gal at 170F (pour water through bag)

0.75oz Fuggles at 60 min
0.25oz Fuggles at 15 min

3 lb light DME at 10 min

Oh and this is a 2.75 gal batch, going to use Nottingham yeast. Stats using 60% efficiency:

OG: 1.071
FG: 1.016
ABV: 7.24%
IBU: 34.56
SRM: 40.00

I went ahead and did this. Ended up with OG at 1.064, so roughly 55% efficiency. I mashed in at 152. It dropped to 146 in 30 minutes and I brought it back up to 150 slowly over the next 30 minutes.

I'm guessing the large volume of water used for mashing may have been the reason I have low efficiency? I ended up using 10 quarts of water for 3.5 pounds of grain because I needed that much to cover the bag.

The other possibility seems to be that my sparging was wimpy and there was significant residual sugars in the water absorbed by the grain. I just sort of poured the water over the bag when it was hanging and squeezed slightly after a couple of minutes.

Still, it should make a nice stout at 6.5%ABV. Smell is pretty good and taste isn't bad but the body seems very light. I may add some maltodextrin at bottling if it's too thin then.

I have brewing all grain BIAB for about a year now. For a 2.5 gal batch at around 7% ABV I actually plug in the numbers for a 3 gal batch ( more trub with BIAB) and I use approx. 8 lbs of grain and plan for an efficiency of 65%. I figure about 2 qts for grain absorption loss and about 1 gal per hour boil off loss. I usually leave 2 qts or so in the pot after the boil so as not to add trub to fermenter, hence the 3 gal recipe.
I have learned to sparge by dunking the bag in 6 qts of 170 F water for 10 min which I then add to the boil water.
My actual efficiency has gone up to 80+% by doing this. I just get a stronger beer but only by 1% or so, which I don't mind.
I also mash over the burner and adjust the heat to maintain the mash temp.
Yours will probably end up drier than you wanted but stick it out and see how it tastes once bottled and given a month. Worst case you learn something. All my batch failures were extremely valuable because I kept detailed records of the entire process.

Thanks, I've tracked it and it ended up at an FG of 1.012. I'm going to let it bulk condition another couple of weeks, but I think I will be adding maltodextrin to this one to up the mouthfeel. It's nice and smoky/roasted tasting (actually with a twinge of sweetness somehow!), but the mouthfeel is very thin.