I wouldn't pay too much attention to that. It's likely a custom dome, but for closer to sea level.
Most engine builders don't like trying to cut custom domes for a motor they didn't build.
You may have to send the specs to Noss and let him cut you a set.
Jeff's prices are already very good for what you get.
ATV stuff is his job, his main source of income, his entire living.
No need to beat him down any more.