Sparge loss.

I'm do a single infusion mash and batch sparge.

My mash tun leaves 2L behind (due to manifold and tap height) plus estimated absorbtion of 0.8L/KG means I get an accurate estimate of first run of.

The problem I have is that th absorbtion and mash tun loss should be taken up from the mash water. So when I add an amount of sparge water, say 20L, i'd expect 20L out. (the grain should already be saturated and the bottom of the mash tun should already be full)
But I'm getting less sparge water out than in. Where's it going?

Is this normal?

I've noticed the same problem. I batch sparge and both the second and third runs are less than what I put in. My guess is the sparge water is hotter than the mash, so some of it is absorbed.

I usually get out pretty much what I put in on my batch sparge, but I do seem to get more out at the end of the batch sparge by raising my drain hose off the bottom of my kettle (but still keeping it under wort). I'm not sure if the pressure exerted by the wort in my now nearly full kettle is enough to counteract the siphon when the hose is on the bottom or what. Maybe I should just try to set my coolertun a little higher in the first place.