Why does EXN (Extreme Natural) Series process lighter at my client's roots and darker on their ends?

Where should I be swatching my client's hair when using EXN (Extreme Natural) Series for the first time?

When using the FRAMCOLOR 2001 EXN Series for the first time, it’s extremely important to match the swatches with the color on the ends. With competitive gray coverage series, the colors have double pigment and are much darker. With the EXN Series, a level 6 is a true level 6, and not a level 4 that is found with most competitive gray coverage shades. Even though a level 6 color may have been used in the past, the shaft and ends may actually be a level 4, thus requiring a level 4EXN to match the ends, or decolorizing the ends to achieve a true level 6 final color.