I am doing 11 gallons tomorrow and with 26.5 lbs of grain, I need 15.1 gallons of water (my post is only 15 gallons). Since that won't work and I really don't want to mash with a lot less water (which I'm still thinking about) I thought I'd use 2 pots to mash in and then mix the 2 to the proper, pre-boil levels to boil. However, that opens up other possible problems like getting the exact amounts of water in each pot.
So, do you think it's better to mash in with less water at first, mash for the full amount then add some 170 degree in after the bag is pulled or do 1 big mash and 1 smaller mash and mix the two? Or do you have another suggestion?
Since I've already crushed/mixed the grains, it's too late to reduce the total amount.......should have thought about that first huh?
My opinion is that splitting the mash is just making things more complicated than they need to be. Like others have said here, when you hit the limits of your equipment and techniques, it is simplest to develop new equipment or techniques.
You could build a larger mash tun and do a more traditional mash/lauter.
You could get a bigger BIAB kettle & bag and continue a full-volume single vessel mash.
You could use your current system and do some kind of modified sparge after you remove your grains to rinse the grains to get the pre-boil volume you need.
You could modify your recipe to do a smaller batch.
Decisions, decisions! One of the things I love about home brewing is the challenge of solving problems like this!