iv been looking in to doing a cpu swap (got to get a 4.1/5.1 first tho ) and fond this page showing different ways to put the paist on and changes in temp
https://www.pugetsystems.com/labs/articles/Thermal-Paste-Application-Techniques-170/
looks like there's not a lot in it GL
As you can see, the difference is just 1-2 degrees. TBH, that's nothing for non-extremes OC computer user.
And the worst 4 result all have the "red area", air bubble virtually means nothing. But all result are roughly the same. Even the thin line method, the paste can't even cover half of the CPU. It can still deliver better result than another 2 methods.
Smooth spread has lots of bubble, but is the 2nd best.
My own conclusion is pick the right paste, choose a method that you want. Do that method properly. As long as the amount is right, the thickness is right, then the temperature should be good (may not be the best).