IR Sensor Replacement
YES, YES, NO

You only need to imagine a flashlight beam width with crosstalk from ambient light.


thus the PD needs a daylight blocking filter and perhaps some carrier like 26kHz for long range and an aperture (heat shrink tubing or recessed flat black hole) to block any stray sources or reflections.
then your emitter (e.g. 26kHz modulation) does not need much current or aperture size to shine only on target.
the absence of light- data pulse on carrier needs a one shot to block AGC glitches after detection (300 ms?)
adjust Tx current to optimum detection/rejection threshold as AGC has a >30 dB range.
easy to find these types used in Remote controls. 
an aperture has a depth and width = tangent cone angle  
choose the desired size to meet your alignment. Tolerances.
I mentioned several variables, you can easily learn how to optimize this to be error free and have several vertical a
For any size and detect a hand, arm or body then ignore for xxx ms or non-retriggerable one shot.