I am also training for a 1/2 in May and my coach recommended the "Alternative Plan" since it adds about 250 calories per day which I have researched and should provide some of that fuel for the endurance. I was under the impression the Athletic Plan was designed for more weight-training oriented exercise vs the endurance needs of someone running for 2+ hours.
My coach also recommeded taking a banana on runs that will last more than an hour. I eat a chunk every 3 miles or so and chug a ton of water after my run. It's going great!
In addition to running 3-4x week, I also have 2 days of yoga. I'm down 22 pounds in 5 weeks, so I don't think the Alternative Plan is slowing my loss down too much.

) and yet my weight remained fairly constant (up/down 5 lbs.
)--the ONLY other thing I could change was what/how I ate. And whoo hooo! It's worked--the pounds are coming off (if slower than I had anticipated or hoped) and I'm still loving my running. AND something new--Hot Yoga!!