Hey.
On the front arches it can appear anywhere along the arch inner (look up), front mud flap upwards, although the main area is dead centre above the wheel, this due to foam padding (larger on diesels).
It's also common for rust to occur at the bottom of the front wing where it meets the sill. Usually on the sill towards the inside edge.
Official line is wings are done FOC, unless previous repair, and there's an official bulletin too. As of this year I believe dealers are also aware of the sills too, or so I am told. Seems to be pick and mix as to what dealers offer before much agro. They don't repair, they replace.