system
A chat on subreddit /r/pcmasterrace
human
I edited to add a random plexiglass video above.  They show bubbles getting trapped the worst in the spread method.  You can only see them briefly before the plexiglass surface is wetted by the paste and looks "good" but they don't have a path to escape.  It's like trying to put on a screen protector or window tint.
gpt
The problem im seeing is that they're applying equal force, at the same time on every corner. So its natural for air gaps to form in this manner. 

When tightening a cooler, you do so in a criss cross pattern incrementally, so that should any air gap develop - its pushed out when tightening the opposite corner... until you're at the end of the threads. 

Even the stock intel coolers that use push clips... criss cross pattern theres no chance that even the pre-applied paste is going to develop air gaps. 

And if you bothered to watch the whole way through... the gap that developed in the middle, disappears.

I betcha if they applied force ONLY on one corner, or on one specific side before pushing on the other corner/side... no gaps would develop.  In fact, I'm willing to place a pizza bet on that.