You're apparently unaware that not all tax appears on your salary receipt. Employers have to pay 20% to SS, on top of the 11% that the employee pays. (This amount doesn't count toward your gross income for IRS purposes though, which is relevant to your point)

The distinction is largely a technicality, all the more because both parts of the SS contribution are paid by the employer directly to the state, but it does have one effect: because the 20% don't show up in the salary receipt, most portuguese people are, like you, blissfully unaware of what the real tax rate on their salaries is.