Strike Water Temperature and Mash Tun Volume

The following picture illustrates a recent discussion I had regarding the strike temperature given by the recipe/mash tab vs. the one calculated by the infusion tool.

I've narrowed the the difference down to the mash tun volume which is not taken into account in the tool. But why should it? The available formula for final temperature prediction when mixing liquids/solids never takes the volume of the vessel into account.

How is this computed in Beersmith, and why?

In a recipe if you have the "adjust temp for equip" box checked then it does factor in the thermal energy needed to heat up the mash tun.  If you don't check that box it will do the straight calculation without adjusting for equipment.  Most of us doing an infusion mash actually do need to heat the mash tun up as well as it absorbs some thermal energy.

Brad