Ok, here is what I found with the Monoprice motion sensor. Note - you can take this sensor apart and put the tape on the inside. I put it on the outside so it was more obvious for this test. In all tests, the sensor was 5.5 to 6 feet high. (Ignore the crack, I dropped my sensor during testing…still works fine, though.)
Test One- Perpendicular to location
In this test, I simulated what would happen if the motion sensor was placed on the wall to the left or right of the location (as in the left or right wall, not the same wall as where you want to sense). If I covered the lens like below, it essentially made the FOV straight in front and to the open side of the lens. Notice I covered about 35 to 40% of the lens, not 50%. I tested with 50% covered and the detection boundary was well past the middle of the sensor, which I found interesting.
Test Two- Shorten the range
Next, I wanted to see if I could shorten the range of the sensor. The lens on this sensor has three different sections. I first only exposed the bottom section, as seen below. This test resulted in me having to be within less than 2 feet of the sensor, probably more like 1.5ft.
Test Three- Shorten the Range 2
Finally, I wanted to see if I could make the range a little further. In this test, I exposed the bottom and middle sections. Range was about 6 feet before I was detected.
Another very obvious solution would be to use a Fibaro or Aeon sensor. These sensors are on mounts that allow them to be aimed in very specific directions. You could use it in the perpendicular wall example and then aim them so the outside of their FOV is at the edge of where you want detection to be. I think these seniors offer the most options. Plus, the Fibaro sensor is AWESOME - motion, vibration, temp, lux! Just read different threads up here.
Anyway, I hoped this help. Maybe there is also a short range sensor as well like you posted about. If there is anything else I can do or test, let me know.