It’s only the same if:
– PAFL is set to default to LR if it’s not otherwise selected
– No other Channel, Return, (Group,) Mix etc has PAFL selected
– The headphone volume is turned up to unity (Not sure if that’s marked)
PAFL setup is in Setup -> Audio -> PAFL.
There is a light just under the LED meters to indicate PAFL being active.
So – Press the PAFL on the mix when LR is selected – and wind up the volume. This will check that the output is working. Then you can work out if the virtual plumbing is in order.
Page 49 of the manual (Section 8.1)