Cubase 9.5 - channel/physical output signal level difference?

Cubase 9.5 users?
I’m experiencing something questionable with my setup while preparing for mixdown/hardware summing. Placing a tone generator on a mono track set to -20db meters on the channel strip at -20db.

However, the DAW’s physical output meters read -23db?

What’s causing the loss of that 3db of gain? & Why is there a difference in signal level between the channel strip and outputs of the software?

Because your pan laws is certainly set to -3 dB…