I saw those two threads. Unless I missed something, I saw nothing in those threads about using a splitter on the top front edge. I like nice rounded fronts like in those threads, but you can't fabricate them with a piece of plywood.
The point of this thread is to get some aero improvement with little effort.
I should add one point. A completely rounded trailer front will direct some of the air that hits it to the sides and some to the top. My guess is that this is ideal. Using just a splitter on a trailer that I described will direct the air to the sides, but none to the top; I'm guessing this is somewhat less of an improvement. The photo you enclose directs the air that hits near the corners, to the sides and to the top. However it depends on having a tractor close in front, as any air that could hit the center of the front surface has nowhere to go. So for a car or pickup pulling a trailer, that solution might not work as well?