Currently, the Microsoft Edge shopping feature allows users to receive notifications for price drops only when a product is discounted by 20% and tracks prices for a maximum of 6 months. Unfortunately, there is no option available to customize the percentage for notifications or to extend the tracking period beyond 6 months. This limitation is part of the design of the shopping feature in Microsoft Edge.
While you appreciate the historical price tracking that Microsoft Edge provides, it seems that the flexibility you desire in setting discount thresholds and tracking durations is not yet available. You might consider providing feedback to Microsoft regarding these features, as user input can influence future updates and enhancements to the software.