Sharpness

In essence, increasing sharpness makes the filter more dynamic which will lead to less filtering.

More technically, sharpness effects how much of a dynamic multiplier gets added to the base filtering value. So at 50hz (IMUF LPF's) it doesn't have to do as much to increase your filtering frequency as it does at 10hz. At 10hz it needs to boost that base filter a ton more to give you more snappy feels and better propwash handling. But that lower base helps by in a sense overfiltering when it isn't a problem and then filtering less when overfiltering would be a problem.