@Mebejedi,
You definitely want the PB on an end with power source or injection point. You wouldn’t want to power a strip at the output side with the PB hanging off the input side without it’s own power injection.
I thought I had written about something like this before, and I found your post from about a year ago!
If you take a look at the diagram I edited you can see a theoretical scenario where a power supply injects in the middle, and I talk a little about the problems this might cause:
In short, yes you can inject in the middle and it goes both ways, but if you have separate power zones, its best to inject power at the edges.