A schematic of what you currently use to test would be useful.
Proximity sensors aren't very sensitive in general. The reflectivity of the surface tends to vary a lot, and any focusing lenses would definitely help.
The other thing to do is to worry about the electronics side - how much the electrical gain is there, and how much rejection of background noise is there. Bandpass filtering at a minimum, synchronous detection if you want to go all-out. Also AGC (automatic gain control) is sometimes used in order to deal with background environments that are too bright.
One thing that you might already know is that usually IR transmitters operate pulsed - 500mA - 1A for a few tens/hundreds of microseconds, followed by a lot of cool down time in between. The duty cycle should keep the average current in the ~50mA range for IR leds, but this depends heavily on the actual LED (i.e. check the datasheet).