Possession is meaningless on its own. Its supposed to indicate how much you have the ball but it can't say anything about what you do with it. Tbh I can't figure out how this possession bonus would work - if its simply added then it is window dressing. Possession should be an outcome not a base factor. Possession would be more meaningful if we also had Territory.

Ofc if a bonus was aactually a performance factor boost (designed in part to increase possession) then it would make sense.

You can get higher possession playing Defensive or Normal or Attacking - just depends on whats facing you too. You can easily increase possession, sometimes, by Whole Pitch Pressing but sometimes that means giving away chances if you get caught with fast breaks so it can be counterproductive.

As far as goal scoring chances go it depends how you count them because goal scoring chances are actually not an easy one to figure out. Shots are just that, they are counted whether threatening or not. Shots on target are not reliable either. If a Shot is directed at goal (ie seemingly 'on target') but is stopped by a player who is not the GK or last defender then its not counted as a Shot on Target stats-wise. So how an opponents defence is set up can markedly affect your Shots on Target.

Personally, I find, when it works as I intend it to, playing defensive with counterattacking can produce a high number of shots on target for the number of total shots where attacking wouldn't (packed defence). But other occasions attacking produces better results. Suck it and see - its not a straight choice between one mentality and the other because your opponent has the same choice.

I can't suggest a way to get more shots because my team stinks this Season >.< but if you find your players more space they'll shoot more.