Error in the results
As you increase the Withdrawal rate, the number of years required before you can retire decreases. There must be an error in the math, as that makes no sense at all.
2 comments

David Johnson commented
Why doesn't this make sense? If you need $40,000 to cover your expenses then at a 4% withdrawal rate you'd need $1,000,000 invested whereas at a 5% withdrawal rate you'd only need $800,000.

gp commented
agreed: "Annual return on investment" and "Withdrawal rate" appear to be swapped.