Except right close to the outflow from the DH, the WB is the same throughout the kiln. The key is that you put the sensor where it gets good air flow and where you can make sure that they wick stays wet and there is enough water.
The DB will be warmer on the entering-air side of the load, and will cool slightly as the air passes through the load. The air cools because it is giving some of its heat in order to evaporate water from the lumber. This cooling means that it is more humid on the exit side of the load, but the WB is the same, entering or exit side.
The DB I’d ideally measuring the incoming air. If fans reverse direction, which is common in a larger kiln, then two DBs are used and the instrument automatically switch’s to the DB on the enter air side.
If you have only one DB, you could find a spot, or even use a piece of 4” diameter pvc with the DB inside. This piece of pvc is located so that it is in air that goes one side to the other of the load without going through the lumber. This way, you aLways are measuring the incoming air. The pipe short-circuits the air flow. Clear?