Look what I found.
A nice sturdy construction and a large storage capacity.

Generation 1

Generation 2

Left picture:
I started out with cutting every other vertical thread on the front lower side to open up the 3 x 6.5cm (1.3" x  2.6") holes to 6.5x6.5cm (2.6" x 2.6"). A little too big for my taste but here I had no choice. I did leaned a piece of sheet metal against the back wall.

This worked just fine the first winter since the hay was pretty stiff. The second year however it did not work at all since this years hay was much softer.

Right picture:
By turning the sheet metal I got it to be steeper. Since the eating grid allways must be higher the the slant I had to cut away more threads to make the eating part higher

Left picture:
I tried to move the slanted sheet metal more to the back to create a steeper angle but it did not solve the problem. Different quallity hay works completely different in these kind of feeders and soft short hay is the hardest too get to work. Regardless of the angle I have found it best to let the slant go all the way to the eating grid.

Left picture:
Hay has a enormous capacity to get stuck on anything. In this case it got hanging in the grid on the sides and did not slide to the front.

Right picture:
I put sheet metal on the sides too but it did still not solve the problem until I made the hay storage more narrow in the back compared to the width of the eating grid.

Right picture:
Here you can see that the sides are moved in to make the storage more narrow in the back.

Right picture:
This is a top view showing the storage being wider at the front.

This feeder was full to the brim four days ago and this is how empty the horses are capable of making now after it have been remodelled.

In our case it is okay if one feeder gets empty since the horses always can go to another feeder but if you only have one that one may absolutely ever never get empty. Everything fails if the horses do not have access to hay all the time.

The truth is that they don't give full effect until the horses have forgotten they ever can be empty.