Getting a little extra paint on this area is a good idea, the lip of the siding is a weak link that can easily peel if not fully sealed. Brushing the lip will work well. An alternative is to <a href="https://www.house-painting-info.com/back-rolling.html">back-roll right after spraying a section of siding</a>. This works well if thee are two people working together.
If you are working alone you can use the airless to deposit extra paint on the siding lip by angling the gun to focus the paint on this area.