Explanation
Decreasing false positives is the best indicator that the information security manager has tuned the system to address senior management's concern that the organization's intrusion prevention system (IPS) may repeatedly disrupt business operations. False positives are alerts generated by the IPS when it mistakenly blocks legitimate traffic or activity, causing disruption or downtime. Decreasing false positives means that the IPS has been configured to reduce such errors and minimize unnecessary interruptions. Increasing false negatives is not a good indicator because it means that the IPS has failed to detect or block malicious traffic or activity, increasing the risk of compromise or damage. Decreasing false negatives is not a good indicator because it does not affect business operations, but rather improves security detection or prevention. Increasing false positives is not a good indicator because it means that the IPS has increased its errors and interruptions, worsening senior management's concern. References:
https://www.isaca.org/resources/isaca-journal/issues/2017/volume-6/the-value-of-penetration-testing
https://www.isaca.org/resources/isaca-journal/issues/2016/volume-5/security-scanning-versus-penetration-testing