Smoke detector wall mounting

I just got the smoke detector for my Simplisafe (current gen) and it so happens that the mounting screws on the wall from my previous alarm company's detector work for this one, so I'm just putting it in the same spot.  

Question:  does it matter how it's positioned?  The "opening" where the test button is faces downward but not perfectly vertical.  More like halfway between vertical and horizontal.  Just wondering if that's ok or if I need to put new holes in the wall and get it perfectly vertical.