There's no documentation but as far as I can tell--
F1-x through F4-x defines the amount of noise reduction or how aggressive the filter attacks the I.F. noise. F5-X through F8-X defines the amount of reduction and the level that's mixed with the filtered and non-filtered I.F. Note that "m" which means "mix" will appear after F5-X and above.
X defines the delay. Delay is the amount of time it takes for the filter to converge on a non-sinusoidal signal or the noise. The higher the number, the longer it takes for the noise to reduce to a low level.