Note that some standards are partialy determined by workability.
A % of butt coverage rule was not workable, even though we wanted more than the minimal thong standard we settled on.
Whereas the overall effect rules give some lattitude to deal with a minmally thongs butt when is is shoved into the foreground compared to the rest of the model, or when the focus of the shot is the crotch even is minmally covered.