Hardware Secrets have tested various methods of applying thermal paste on CPU and tested for their temps. In the end, they confirm what we probably know for quite some time - a small/tiny dot at the middle of the CPU is the most efficient way to get good thermals, no need to spread it all around.
Link:
What is the Best Way to Apply Thermal Compound? | Hardware Secrets
Link:
What is the Best Way to Apply Thermal Compound? | Hardware Secrets