My Subaru XV has the center camera (behind the rearview mirror) like in these
pictures. So if I mount it like what he did, it would be around the mid-height center of the windshield. Is that the optimal place for my case? Or just place it on the left side on the back of the rearview mirror?
The A129 has a different form-factor and would not work well where the BlackVue in the pics showed. You should consider things in this order:
1- Is the cam within the area my wipers will clear in the rain?
2- Is the cam going to interfere with my driving view to a degree where my safety is compromised?
3- Is the cam going to interfere with a car function?
4- Can I see the indicator light of the cam to know it is working from the driver's position?
5- Can I easily reach buttons I might need to use when driving?
6- How visible is the cam going to be from outside of the car? (Helps to deter theft)
7- Can I see things on the screen of the cam like parking mode and recording indicators? (Not really necessary but good to do where possible.)
And in all this, remember that the cam and cable needs to be removable from the mount, and when it can happen the card should be removable from the cam with it in the mount.
If you are considering which cam to buy, get it's dimensions from the website, cut a piece of cardboard to that size, mark on it approximately where the buttons and indicator lights are inside and where the lens is outside, then temporarily tape your cardboard model to different places as a test with you sitting in the driver's seat normally. Think about cable and mount removal space, and remember the cam has thickness your model won't have which might interfere with mirrors and such.
This should help you find what the possibilities are and guide you to the best location for that cam in your car. If you can't find a good location consider a cam with a different form-factor which might work better for you. Above all, never compromise your safety by having the cam block your needed view while driving. The whole idea of a dashcam is to enhance your driving safety, not to lessen it.
Phil