Bob, nice job answering his question there :/
For boil in bag meals I hardly use more than 1.5 cups of boiled water. I like my meals a little thicker (less runny means easier to eat) so even for MountainHouse 2-person meals that require 2 cups, I still stick with 1.5. That said, I find a 450ml to 600ml cup to be perfect.
Edit* just saw your new post,. By Andrew Skurka design, are you refering to the catfood can stove? That stove is pretty wide, so mugs won't do a great job capturing the flames, as most of the flames will come out from under the bottom of the mug, and up the mug's sides, losing efficiency. You're going to want a wider pot for a stove like that.
Personally I'm an advocate for the trail designs caldera keg. When I use esbit tabs, my setup weighs less than 3oz (pot, stove, windscreen). With alcohol, it's not much more either. Not as cheap as a DIY cat can, but the whole setup will likely be lighter and more efficient.