I am Marine FC in the Conference North and right now I can't even get 30% possesion on certain teams. I'm playing "Retain possesion" and "shorter passing" too!
Perhaps you can take a look at how he set it up and try to see what you can apply to your own tactics. I did that and I'm also getting a resonable amount of possession for my tactic.
Retain possession, short passing, work ball into box, play out of defence, run at defence, deep defensive line, hassle opponents, offside trap, lower tempo and more disciplined... Try this with a 4141 formation (anchor man and 2 inside forwards), and train your tactics intensely. Will take a while but I guarantee you'll see signs of progression when it comes to your possession stats and passing completion percentage! Hope this helped...