Let us assume you are using an ordinary inferred LED and a type of inferred detector used in remote control entertainment equipment.
Inferred LED modulation is simple and is well documented on the web.
The inferred receiver is a complex device. It contains, among other features, an Automated Gain Control (AGC) circuit and a Phase Locked Loop (PLL) circuit. The AGC adjusts the gain and makes it impossible to gauge the power of one IR source relative to another. The PLL "locks onto" the signal.
Consider using and adjusting the power of a secondary inferred LED transmitter transmitting at the same time as the primary LED transmitter is being received. The secondary inferred LED transmitter is local to the inferred LED receiver and transmits a unique code. The primary inferred LED transmitter is part of the opponent's equipment and transmits a unique code. Slowly reduce the power of the secondary inferred LED source until the code switches from the secondary source to the primary source. The power used by the secondary inferred LED when the switch occurs should be proportional to the distance to the primary inferred LED.
In the above scenario we have used the AGC to "hide" the primary source until we reduced the power of the secondary source to just below that of the primary source. And we used the PLL to "lock onto" the strongest signal.