Mash in Keggle - False Bottom vs. amount of mash water

I plan to do my first all grain batch this weekend, so forgive me if this is a stupid question.

I have a SABCO false bottom that sits a couple inches above the bottom of the keg (as it is supposed to). Therefore, approximately 1 to 2 gallons of water exists beneath it. (maybe only 1, I havent measured yet).

My quesiton is as follows:

If my recipe calls for a 1.25 quart to 1lb of grain ratio, whats the deal with the amount of water required to reach the bottom of the grain?

Do I start my 1.25 quarts/1lb ratio AFTER i reach the bottom of the grain bed, or do I just use a straight 1.25qt/1lb ratio, and not worry about the water that wont contact the grain bed? If I do the latter, after I mash out, will I still have water sitting on top of grain bed?

I think this is called "dead space" and you can correct for it in beersmith under water needed. But yes, you have to add this to your mash in water. I think you subtract from the sparge though to get correct volume assuming you can pick up that liquid during transfer to boil kettle. I don't have a false bottom, so I'm only throwing out what I've read on the site.

I'd measure the deadspace from the false bottom and then add that volume to your strike water amount. It should be fairly minimal.