Rotate the rear derailleur as far rearward as it will go. AKA, clockwise around the mounting bolt. Then tighten the mounting bolt. That will ensure that the tab on the RD is properly behind the tab on the hanger.

As for the M772 and its cable loop, by the design of the RD (which Shimano calls "Shadow") the cable run will be straighter than a conventionally-designed RD.
You can see on my bike, the cable comes out horizontal from the cable stop on the chain stay, bends up a bit and then back down into the RD. If your cable stop is on the seat stay (common on 'cross bikes and MTBs), then the Shadow routing is even straighter.


As you noticed, the Shadow RD doesn't have a cable adjustment barrel. So, you'll probably want to install and inline cable adjuster somewhere. On mine, the downtube cable stops have an adjuster. On another bike, I use a Jagwire inline adjuster.