This is accurate except for one thing. If you are using the same boil kettle or ones that aren't much different in diameter, then you don't simply double your pre-boil volume because of boil-off rate. If you are using a kettle the same diameter or close to the one you use on your smaller sized batch then your boil off does not double. If you simply start with double your water then you will have too much and too low gravity in your final batch. For example, I do mostly 5.5 gallon batches and they start out as 8.4 gallons for a 90 minute boil with my system. If I double them, then I get 11 gallons (double the final volume) and start with just over 14 gallons (not double the original volume). If I doubled the preboil volume then I would have almost three extra gallons of water. The difference will depend on the different surface areas of your boil kettles--with a bigger surface area more boils off. My small kettles are only a little smaller in diameter than my large kettle, so there is not a lot more boil off in the same length of boil.
In case you are wondering, I ran this through some of my recipes in Brew Smith and when doubling a batch, it did not double the preboil volume, but adjusted it for my system parameters. I always double mine this way and hit my gravities.
The only time I double my preboil volumes is when I split the large mash into two 5.5 batches and boil them with separate kettles and burners.