The statement that accurately reflects the concept of a Significant Audit Difference (SAD) nominal amount is:

The amount we select for our SAD nominal amount has an effect on setting scopes and thresholds.

This statement acknowledges that the SAD nominal amount, which represents the threshold for identifying and reporting significant differences during an audit, influences the determination of audit scopes and the level of testing required. The other statements either describe actions related to planning materiality (PM) or present incorrect information about the minimum percentage for designating SAD nominal amount, which is not universally fixed at 5% of PM. The communication with those charged with governance about changes in SAD is important, but it depends on the specific circumstances and the audit firm's policies.