RSSI radio values not matching GCS

[rsilk49]

I have Frsky X8R paired with the XJT module. The RSSI port on the receiver is connected to the SBUS port on the Pixhawk as per Arducopter docs (RSSI_ANA_PIN = 103). The hi voltage setting in Mission Planner (RSSI_PIN_HI) is set to 3.3v.

For example,

1) radio shows a RSSI value of 90, but Mission Planner shows rxrssi 90-100.
2) Radio shows 45 (low warning), Qgroundcontrol shows RC RSSI 66%

Pls note, these tests are for the radio receiver RSSI, not the telemetry RSSI.
It would appear that the reported receiver RSSI values on the radio are somewhat lower than Mission Planner and Qgroundcontrol.
I am assuming all numbers represent a percentage of full power . . .
Anyone have an explanation?

.rs

[Kilrah]

Values are likely a completely different scale. I believe in ardupilot it's a percentage, but on FrSky telemetry it isn't.

[rsilk49]

A few more recent observations:
I now have Arduplane running on a Matek F405-Wing. I have set the Arduplane rssi params:
RSSI_TYPE 1
RSSI_ANA_PIN 15
RSSI_PIN_HIGH 3.3
RSSI_PIN_LOW 0

The rssi signal lead on the X8R receiver is connected to the rssi pin on the FC. The receiver is connected to the FC via SBUS.
The radio has an internal XJT module.

The ground station (qgroundcontrol) shows rssi levels in the high 90s when the radio is close to the receiver. I believe the unit is a percentage value.
The RSSI level on the radio shows levels in the 80s.
Is there any way to get the 2 readings to match?