So I've looked around some threads, done a search, looked through my various books and I finally accept that I'm just going to ask the question...
I generally do a mash ratio at around 1.33. It's a nice middle ground and I've been happy with the results generally speaking. But here's where it gets complicated...
I have a Coleman 7 gallon cooler/mash tun. I was using a stainless braid with it, but that was giving me some stuck mash issues. So, I put together a simple PVC platform with a custom-built screen over the top to serve as a false bottom and keep the grain off the braid. It works great.
However, I need about 1.5 gallons of water underneath the bottom to bring the level up to the base of the screen. (problem due to the placement of the thermoprobe. I have to have the false bottom a little higher than I would have liked it otherwise.)
Anyway, I simply fill the tun up to the base of the false bottom with liquor and then add my mash volume along with my grain. This keeps my grain hydrated at the proper amount BUT, since I run a HERM system, I technically have a lower gravity after my mash than I am expecting. This isn't really an issue since I match my sparge amounts as well as I can and then boil down to my target fermenter amount. (Ultimately, it comes down to math and I have a spreadsheet that pretty well spells it all out for me.)
My question is sort of just academic... Is the mash ratio water amount expected to be in addition to the liquor underneath the false bottom (I assume so, otherwise your mash would be too thick.) and if so, are there specific formulae that take your 'under-bottom' liquor amount into account when figuring the expected pre-boil gravity?
It could be this is just one of those 'learn your equipment' things. Like I said, I either adjust my sparge amount to account for the extra liquor in the first runnings from the under-bottom or I boil down as necessary and do the math from either of those two points.
ideas and input welcome. I've just never seen any specific discussion of under-bottom liquor amounts and how that relates to your mash and sparge volumes.