I know this is really old, but I just figured this out earlier this week. If you go into the list of standard mash profiles (through the "Choose" button on the recipe editor), you can edit the the initial settings. I think they're all based on a 10lb grain weight. Adjust the Mash Out volume until the temperature ends up near boiling (I just used 5qts at 210 to account for a slight temperature drop during transfer). Then, when you select that profile, it will automatically set the mash out volume based on that water temperature.