What about people that are just physically larger than average. I’m not excessively overweight, maybe 30 pounds at best. Losing that weight isn’t going to change my structure, which quite literally is larger than the space allotted in economy class (my shoulders are wider than the space is), which forces me to lean to the side if someone is seated next to me to avoid encroaching on their space.
Take height into account. BMI might get it done best