I have the upside down mushroom kind that attach by a round shaft that allows it to slide up and down inside a larger diameter shaft which is attached to the blade. The shaft has a hole drilled in it and you can adjust the shoe height with some large washers by either placing them above or below the sleeve. (A picture really IS worth a 1000 words!) Probably clear as mud by I plow a lot of snow on a combination gravel/blacktop/grass and I''m glad I have them. Saves the grass, saves the blacktop, and allows me to NOT push all the gravel onto the grass!
Also works great for laying a uniform layer of loose material down like sand or gravel. Just set the shoes to leave a 1inch gap and drive. Presto - you have a perfect 1 inch layer left behind. (Can't do that with a box blade although you COULD if it had skid shoes or guage wheels)