If say that if the pit size and a slim profile is critical, then the HWM isn't the jacket for him. Most of their other short jackets, particularly the new ones, are a slimmer cut.
IGNORE TAGS.
As to the pit to pit numbers, the general rule o' thumb is pit to pit, x2, minus 4.
So, 21" pit to pit, x2=42". Minus 4" = 38. Size 38 jacket is as such.
The other thing to look out for here is the drop between the pits and the waist. You might fit fine in the pits, but have a really skinny build and have this potato sack-looking jacket when done. If you're waist measures a true - NOT TAG - 34", then note that in the jacket size. You'll want to compensate and have it tapered - assuming you want it that way.
Found one for sale on Aero's page but it has some weird measurement.
38 Tag
SHoulder - 19
Back - 25
Waist - 21.5
Pit-Pit - 23.25
Pit-pit seems oddly large. All the other measurements are good on this jacket and will fit me. I really need a 21.5 pit. How bad / loose would this look as is?