2.5 for the mash thickness is fine.. we're talking BIAB here.. a mash thickness of 3 is considered normal
That was my point. I forgot to quote the post I was responding to. It was this one.
This has been bugging me and I finally figured it out, I think. Your water water far too little. BIAB is usually done with all the water used in the mash process, including sparge and water absorbed by the grain. At 4 qts per pound (2 for mash and 2 for sparge), 13.25 lbs of grain requires 13.25 gallons plus another 6.5 qts or so for the grain. That surely affected your efficiency.