Flaked Grain water absorption

I did some searches but I couldn't find a definitive answer on the rate of mash water absorption for an oatmeal stout. I made this recipe once before and it's real good but I mashed in with a water volume based on the entire gran bill and the beer was a little thin IMHO. I think the mash volume should be reduced to account for the 3lbs of cold steeped grains. I normally mash at a ratio of 1.5qt/lb of grain but wondering if 22% of my grain bill is flaked grain changes absorption enough to take it into account.

The mash grain bill will be: (10 gal finished batch)

14lb 2 row
2lb C-10
4lb flaked oats
.5lb flaked barley
Mash for 90 min @ 154F

I will also cold steep (2qts/lb grain) and add steeped liquid to the last 10 min of the boil

1lb Carafa III
1lb Chocolate
1lb Roasted Barley

 

Mash volume doesn't have much effect on the efficiency if you are mashing for 90 minutes. What was the OG?

 

my OG was 1.053, Beersmith estimated my OG at 1.055 and measured my mash efficiency at 75.8%

It finished a little high at 1.018 and Beersmith estimated 1.015. I write that off to using 2 packets of SA04 a full year beyond the expiration date on the packets. My inventory control (using oldest ingredients first) messed up there.

When I said the beer was thin I meant mouth feel.

I still would like my original question on grain absorption answered if anyone has an idea.