Depends on how far down you want to go with all the people sizes in all the various combinations of positions. I imagine the cost-benefit is based on the margin

Depends on how far down you want to go with all the people sizes in all the various combinations of positions. I imagine the cost-benefit is based on the marginal change of information you get by changing the dummy size/shape, and based on their revealed behavior, they don't think more sizes add more information.