I am wondering what the Reverse Received Signal Strength Indicator (RSSI) is. I came across the term in the BEEKS Beacon's datasheet, under the heading "Bluvision BLE Stack Specification".
This doesn't appear to be a common term outside of Bluvision products. I would contact them directly.
My best guess is that their product, when acting as a peripheral, will send the central an RSSI value in the response to the central's scan request packet (since they mention this feature in the context of advertising). That RSSI value is the signal strength of the central's scan request packet as heard by the Bluvision sensor.