Aneros psy adjustments

Just need a bit of information. Not seen it mentioned here but have seen vague mentions on Reddit..

I want to verify which arms do what, from what i've seen the p-tab (front arm) controls depth and angle the rear however controls impact depth? 

Also how close should the p-tab be to the anus? As I currently have it set to just past the groove where it dips by my anus so I assume it's where the perineual triangle but I'm confused slightly about what the front arm controls and what the rear one controls.. mainly I just want to confirm what I suspect based on Reddit posts and how I should best assange the arms and how far away from the anus I should contemplate moving the p-tab while making sure to keep a safe amount of pressure on the prostate.