The dress shirt is too tight at the stomach, causing it to pull uncomfortably or simply look unflattering. This could be a problem at all times or primarily when sitting.
The answer to this problem is fairly straightforward: increase the midsection width of the shirt. This will provide more fabric around the belly, reducing any uncomfortable tightness there as well as allowing the shirt to drape more flatteringly around the midsection.
How the adjustment works
Increasing the midsection width by 1/2″ increases the midsection circumference by 1″. If you have “default bottom width” selected, the system will typically increase the bottom of the shirt the same amount, but you should take care to consider this adjustment as well.