Click "wrote about a report", then in that article click "new report", and you'll find this:
"The signature finding of Out of Reach is the annual Housing Wage - the hourly wage a full-time worker must earn to afford a decent two-bedroom rental home at HUD-estimated Fair Market Rent (FMR) while spending no more than 30% of income on housing costs."
It is not at all obvious. I really wish that news articles like this would set aside a section where they explicitly name and link to their sources rather than burying them as hyperlinks in the text.
Yes, it really seems like a variable approach would work better. There's a big difference between spending 30% of your income on housing while living in a rural area and doing so in the middle of Manhattan. I imagine that percentage could go considerably higher in big cities.