There are differences between RFID tags. Some are designed to be cost-effective and versatile. Others are optimized for specific applications. How well a tag functions in a given application depends on the used IC, antenna, and matching circuit, as well as materials surrounding the tag, and other enviromental factors.
The established approach in the RFID industry and academia is to look at forward link and return link performance separately. The forward link is limited by power transfer to the tag, thus the key performance parameter is tag sensitivity. The return link, in turn, is limited by detecting the signal scattering back from the tag, thus the key performance parameter is the backscatter signal strength of the tag. These parameters are typically measured as a function of carrier frequency, orientation angle, substrate etc.