Dear KnewHow. A lot of quality contemporary coffees are designed for extracting a lot less than "a full espresso cup" which could well give you an over-extracted sour result. My first stop would be trying for a fair bit less than 1oz over 23-25 seconds. I wouldn't be moving your extraction pressure anywhere away from 9b. Again, contemporary coffees are designed specifically around this extraction pressure. We experimented moving our pressure both up and down and the Italians got this right 50 years ago.