One Too Many
If your actual chest is 42” a size 38” highwayman might look like it’s got a p2p that works ok but then it’s going to feel small in many other places (the neck hole is way too tight, the front pulls… etc.) .I might be a bit slow today. But, what do you mean?
The highwayman has very low armholes making the p2p measurement not that useful imho.
I’ve owned 4 highwaymans. From 2 size down up to my standard chest size. I don’t feel like recommending to size down 2 is the right approach unless you plan to only wear it open or half zipped with a single thin layer underneath.
Anyway, speak to the people at Aero and firm up your measurements or that of a jacket that you feel fits fine.