The Sky Shark models use larger engines for the higher altitude that they fly at. So the power recommendations are good for people who live in or around the mountains.
As far as Brian Taylor is concerned, he always powers his designs on the low side. To keep the flying speeds near scale. His models build very light and scale. Depending on where you live, a 1.20 might be okay for the BT plans. You can always pull back the throttle.