Why would the clothing equation have to be more complex than...
(Surface of Area of wearer measured in fractional square yards) S
times
(Culturally or Environmentally mandated coverage area, expressed as a percentage of wearer total body surface area) P
times
(Weight of preferred (potentially multi-layered) fabric measured in fractional square yards) W
with a small percentile addition for buttons, buckles and insignia.
...?
( so my Hard Science mandated equation would be... Fabric Yardage Weight, Y = S * P * W )
I think the inverse square law only applies to solid objects. Not their wrappers. The private parts of a giant don't require thicker fabric to maintain decency... only more of it.