If he had a standing job for the last 15 yrs ,then it should be considered. They go by the last 15 yrs,not a flipping hamburger job or delivering newspaper job he may have had 30-40 yrs ago.
His education makes everything alittle dicey but if he can't stand or sit for 6 out of 8 hrs ,what jobs would there be that don't require standing or sitting. Maybe a bed tester job at Lazy Boy-but those are far and few.
His attorney is best equiped to answer most questions.
And don't forget the pain factor. Albert Einstein would be considered disbled he had trouble thinking,standing or sitting because of pain.