I just revamped my system and went from a 70 qt Coleman Xtreme with a Bazooka screen to a 20 Gallon Kettle with a false bottom. In ironing out the bugs of which I became aware on my inaugural brew, figured out that the false bottom sits about 2.25" above the bottom of the kettle, which amounts to roughly 2 gallons of strike water that isn't in contact with any of the grist until I begin to recirculate (usually about half way through the mash or later).
For a 10 gallon batch with a grain bill in the low to mid 20 lb range, I mash in with 9 gallons of water and batch sparge. When I did this on my first batch on the new system, my mash temp came in low and the water to grist ratio was way thick. I added about 1.5 gallons of boiling water to get my mash temp up and extended my rest by 30 minutes. In the end, all was well, but it is obvious that I need to account for this.
So my plan is to simply add 2 gallons of water to my strike water, adjust my mineral and/or acid additions to the mash based on the total gallons of strike water, i.e. 11 gallons, but treat my water to grist ratio and strike water temperature calculation as if I were only using 9 gallons of water since the grain isn't going to come into contact with any of that water beneath the false bottom until I recirculate, and, presumably, at that point, most, if not all of my conversion is complete. I would reduce my sparge water volume by the 2 gallons I added to the strike water. Does this sound like I'm on the right track?
Alternatively, I could always rig up a bazooka screen to my kettle dip tube and eliminate all of this adjustment. If I went this route, has anyone run into issues recirculating/transferring with a pump using a bazooka screen in a mash tun?