A LogTag data logger will record the temperature (and humidity of applicable) directly adjacent to its sensor. The logger has no "radius" or "area of coverage", and we cannot advise how many loggers will be required to cover a certain area.
How representative the measurements are for an area (or air volume) depends greatly on several environmental factors, including, but not limited to, air movement and obstructions in the area a logger is deployed. There is no set rule that can cover this.
If this is critical to your operation, we recommend to get a laboratory to undertake a mapping study, where multiple loggers are put in the area to be monitored.
The number of loggers and the ideal positions for them to be located can be determined on the basis of any variation noted in the mapping study, and how critical temperature or humidity are for the product being monitored. It will also tell you how representative the placement of your logger is for other locations in the area.
If you own multiple loggers, you can undertake a mapping study yourself, however, we recommend to leave this to an expert.