Motion sensor IR vertical coverage

I searched and did not find this answer. Apologies if I missed it! I need to mount a motion sensor on a staircase post pointed at an entry door. Unfortunately a magnetic door sensor is not currently an option to monitor the door. I tested this with a 1st gen sensor mounted normally (i.e. "right side up") about 7" (inches) from the floor and it seemed to work well. It's 6' across from the door opening. I tried upside and it also worked - but difficult to tell if it's more or less sensitive. I could not find documentation on the vertical span of the PIR sensors. Since the devices are intended to be mounted about 7' high, does this mean they are built to point slightly downward when mounted flush to the wall? If yes, then I should probably mount the device upside in my case. I've ordered a 2nd gen sensor to test with as well. It will be a little less conspicious and if all things are equal, I will go with this choice. Are the 1st and 2nd gen vertical sensor spans identical? Thanks very much. I hope this information is useful to the next person that's interested in this.