Setting up equipment

Hi,
I'm trying to set up the equipment, I use for brewing, but some of these terms are confusing me.
It is possibly due to being in english (I'm danish), and probably also due to my inexperience (only done 1 brew so far).

But, this Mash tun volume, seems to be messing with me. My recipe says I need to sparge -16 liters, so obviously something is wrong.
Can someone help me with the setup?

We have a 29L boiler, which we only really fill 25L into.
The fermenter is also made for 25L.
We do everything in the boiler, and simply have an inset, with a grate in the bottom, that holds the malt. When we don't need the malt in anymore, we pull the inset, and top off with water.

BUT, I can't seem to figure out, how to replicate this setup, in the equipment.
I have tried to set 'Top up water for kettle' to 25L and 'Batch volume' to 25L.
Mash tun volume, I am unsure. Should it also be 25L?

The batch volume is usually set to the amount of cooled wort you put into the fermentor with the yeast. 

To that final amount, on the Equipment profile page, you add back for any losses (trub, boil off, etc.), and for your case, you may want to "uncheck" the box that makes BSmith calculate the boil volume since you know it is 25 L. 

You may find it easier to ignore the top-off water entry, and just focus on the boil-off rate until it makes sense for your pot.