How does Fusion decide how much swap space is needed when i create a CentOS guest

I am using Fusion 7 on MacBook Pro with 16GB of RAM on OS X Yosemite. I created a VM with 4BG of RAM, but I got only 1983MB of swap space. I created another VM with 2GB of RAM and got 3999MB of swap space. Is there a formula to follow? Thanks.

Here is what I found on CentOS document on swap space rules:

https://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-swapspace.html