Water to Grist ratio

My mashtun is a 40 Gal (approx 150L) stainless steel kettle.  I made a false bottom for it that has around 3.5 Gal (approx 13L) of liquid under it.  This is not “Dead Space” as my setup allows me to drain almost all of that out at the end of mashing. The normal brew length is 31gal (120L) and I typically mash around 60 pounds of grain (27kg) into 19 gals (71L).

My question is how do I account for the 3.5 gals. of liquid when calculation the water to grist ratio? 

I read somewhere that the ‘stiffness’ of the mash has an affect on the sugar profile.  Is this literally the ‘stiffness’ of the grains above the false bottom or is it all the liquor in the mashtun?

I consider it all one volume.  It's not like it is completely separated as the water does get moved around especially when any recirculation takes place.