Russ' ability was incredibly strong, but from the beginning since he had it, there was always something he struggled with, and that was estimating how many MC cells would be required to use his ability.
When using his powers, it often depended on the other person's mind, how strong the image was of their skills or their powers. The stronger the image of power they had, the stronger Russ was and the more MC cells it would use.
There were times when they thought of themselves as weaker than they actually were, which would put Russ in a difficult position, those that had an accurate representation of themselves and those that overvalued themselves as well.
Because of all these reasons, even if Russ had seen the power in question and the level of strength they had, it was still hard for him to guess just how many MC cells would be used, especially if they were hiding a big part of their strength.