The rated IR distance is measured in total darkness, against a target of roughly 90% reflectivity, with the beam angle matched to the lens field of view. Falling short on site is normal. The main variables are:

• Beam angle narrower than the field of view: the edges of the picture receive no IR, which reads as insufficient reach.
• Low target reflectivity: asphalt, vegetation and dark walls absorb a large share of the IR energy, so brightness falls off sharply with distance.
• Atmospheric scattering: fog, haze, rain and snow scatter IR strongly; the poorer the visibility, the faster the roll-off.
• Insufficient supply voltage: low voltage silently reduces emitter power, most noticeably on long power runs.

For selection, choose a model whose rated IR range is at least 1.5 times the distance you actually need to cover, keep the emitter coaxial with the lens, and leave headroom in the power budget. Where colour detail matters at night, a starlight low-light model or white-light supplement is the better answer.