IRS is correct per https://www.irs.gov/businesses/small-businesses-self-employed/understanding-penalties-and-interest

Income tax returns are subject to a minimum late filing penalty when filed more than 60 days after the return due date, including extensions. The minimum penalty is the LESSER of two amounts – 100% of the tax required to be shown on the return that you didn’t pay on time, or a specific dollar amount that is adjusted annually for inflation. The specific dollar amounts are:

• $210 for returns due after 1/1/2018
• $205 for returns due between 1/1/2016 and 12/31/2017
• $135 for returns due between 1/1/2009 and 12/31/2015
• $100 for returns due before 1/1/2009