No the knives are stationary and are in the same height as the retractable ones when they are all the way up. We haven't noticed a situation where we would have to have them any lower than they are. I think having an angled knife helps lower the horsepower needed to cut up the straw.
I forgot to add that these knives are a 1_4 inch thick so they last a lot longer than regular sickle sections. If you do happen to break one it is three bolts to replace the broken blade.