Hi,
1. thought mine opened more at 22-23 but then for the rest is seems to stay stationary; perhaps thats because the air temp is not changing, unlike actual motoring/heating
As far as I remember when I looked, the other motor changes the air flow direction according to the mode selected.
2. When testing for heat I would set the direction so the single horizontal Arrow shows and its pumping the air out of the two main central vents by the radio and Auto Off
Have read before with folk having heating problems that the passenger side can get warmer, assume that must be that the air can get out easier at that side or as you say the matrix is getting some heat on that side. Not aware that it a dual zone climate control as you would need two setting on the controls.
3. Think it sounds like you need to unclip those matrix hose pipes in the engine bay and attach some hose to one pipe and say using a funnel pour some water down and see if it readily flows out of the other side.
4. One thing I have read about on A/C cars, think it was an article in Car Mechanics that sometimes the damper flap, though the shaft is being turned by the motor or manual control, the actual damper flap is slipping on the shaft and staying shut; thouggt I was getting something like that at one time, but seems to have corrected itself.
Have sent you a PM with some more info.