PMP22650: Stackup | Number of Power Layers

Dear all, 

I have a curious query to which I often get the answer as "Based on experience"!

I wanted to know the below - 

1. How do we decide on the number of power layers in a design?

2. Is there a methodical way to arrive at this number? Say, 3 layers, 4 layers, etc

For example, for a 1 kW, how many power specific layers are required?

For a 6 kW, how many power specific layers are required? What is the math behind that number of layer selection?

Can you please explain with a detailed example?

Warm regards,

Siri