I wear full shin and knee pads under my calf cuffs, if anything I feel more comfortable and secure, not only can I pull that strap as tight as it will go, but the extra padding from the pads gives me plenty of comfort, I wore my bocks for 6 hours without the pads on and soon had painful bruises on the sides of my calf from where the end of the bolt is under the strapping, but that's an adjustment issue, move the bars a bit wider.
To answer the question full shin and knee are wonderfully comfortable, I actually use 661 downhill mountain biking race pads, fairly expensive but they have saved my bacon on my bike many a time and barely show any wear and tear. Not yet fallen off my bocks at all which is good.
Good luck with your decision!
~ Samarka