I have a 1440p monitor and usually browse in a window about 640px wide (monitor split into four columns). The popup covers a very large chunk of the actual text.
And it's not "a chat message" on top of that, which is what makes my eyes roll out of my head and bounce down the lane. It's a CRM feeder pretending to be a chat application, where it's more likely than not there's no human on the other side and it's very likely it's not the person whose name is on it. It's just lame and manipulative stuff Marketer Stuff.
And it makes business sense as it usually increases engagement and interaction with potential customers.