Why am I having challenges achieving cool reds with gray coverage when using FRAMCOLOR 2001

Using EXN (Extreme Natural) Series versus NP (Natural Perfect) Series: What is the difference?

To make the coolest reds when covering gray, the EXN (Extreme Natural) Series must be used instead of the NP(Natural Perfect) Series. The NP Series contain yellow, which warms the cool red tones. The EXN Series are cooler with a blue-violet base, thus keeping the red cool. The CB (Cool Brown) Series can also be substituted for the EXN for the coolest reds ever because they can also be used alone for gray coverage.