It actually makes sense that the multiplier is lower at the lower end.

Expenses like food, hellth in$urance, car, commuting are basically fixed regardless of income, so you have less disposable money to spend on mortgage payments.

If you go out to eat 1-2x per week, it’s not going to change your expenses much whether you’re spending $20 or $100. Same with a car costing a few hundred extra per month.