I am just sitting here and rereading your post and I am trying to recall where I read about all the plow types. Some old publication I had read had a writeup about all the various mouldboard designs and the soil types they were designed for. There were the really short mouldboards that you write of, the intermediate that seems to be most common here in New England, and  some really long ones that as I recall were designed for virgin prairie sod.(am I wrong?) There were also slatted ones that mystify me.... I was told they were for heavy clay soils.  
   On the farm I worked on as a kid, we would often borrow a plow from a neighbor which they called a brush plow. This plow was on steel wheels and had a single mouldboard, perhaps 16 inch and very long and very long plow points. The big difference was that instead of a coulter out in front, it had a single fixed vertical blade that cupped over the plowpoint at the very tip. We used this to break open new ground. It would rip up roots and stumps up to 8 inches. Needless to say, as a kid, it really impressed me.   
 I guess the mouldboard used depended on soil type, or what type of trash had to be covered, i.e., wheat stubble or cornstalks and probably personal preference.
I will try to locate whatever it was that I read about the plows.
                             Cal