Normal
Even on MI systems, I think just about all of this is true. One of my best hints for dealing with mud is to think of cutting harmonic sequences instead of single frequencies. Instead of cutting 500 by 6 db, try cutting 250, 500, 1000 by 2 db, and then sneaking a little of the top sequences back into the mix. I usually find the mud is where multiple sources all have first or second harmonics.