IMHO
AnalogWrite(x) is 100 * x / 255 % duty cycle
=>
AnalogWrite(0) is 100 * 0 / 255 % or 0% duty cycle
AnalogWrite(255) is 100 * 255 / 255 % or 100% duty cycle
AnalogWrite(63) is 100 * 63 / 255 % or 24.7% duty cycle
AnalogWrite(64) is 100 * 64 / 255 % or 25.09% duty cycle
So I think 64 maches better to 25% than 63
Best regards
Jantje