There are more differences - ears, nostrils, eyelid creases, eyewhites.

Did you use material-based AO for the first render?
And did you switch off raytracing for the second one? (I know you said same render settings... just checking!)

Could that be the difference, rather than the type of shadow you are using? Not sure....

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)