Cousin David: Your flash photography of David (my son) inspired me to do my own experiments. I used a hallway so I have left wall, right wall, and ceiling as reflector. The experiment spreadsheet is attached and the results are posted. I used evaluative metering for camera and ETTL for flash. I did not try manual exposure and flash setting.
Left and right wall still remain unbalanced relative to one another. 45 degree up is more pleasing but you notice the top of the head is lit more. 60 or even 90 degrees up would probably throw more light onto the front of the face.