Drive IR LED with maximal power (for IR barrier with max distance)
As others have suggested, beam spread is likely to be your problem. Most digital cameras will detect IR to some extent. (Try pointing your TV remote into the lens of your camera and press a button.) You can try using this technique to see what's going on.


Draw some concentric circles on a sheet of paper - maybe 1 cm apart - like a target.
Set up your IR LED some distance from a sheet of paper - say 30 cm.
Set up your camera / phone to view the sheet of paper. A quick test with my HiFi remote control showed that it does transmit through office paper so you could test from either side.
Lights down, cool jazz music on.
Using the camera, centre the IR beam on the target.
Try putting any lenses you can get your hands on in between the LED and the target and see if you can focus the beam any better. Camera lenses, spectacles, magnifying glasses, etc. A quick web search for DIY concave lenses got many results including some for turning them out of acrylic rod in a drill chuck.
The object of the exercise is to narrow the beam angle and reduce the diameter of the IR light spot.


Have fun.