On Airstreams, due to their rounded roofs, we often use different sized feet to attach the solar panels to the roof. Some clients like to have the panels conform to the curvature of their roof, others prefer a more level appearance. We are happy to install them either way, or even come up with custom mount sets when necessary. This client asked us to use taller feet on the outside, and shorter feet on the inside, resulting in a flatter look. At the end of the day it’s only about personal preference as the performance difference is generally negligible.