Now I have decided on my openings, it is just a matter of time to master them. With daily exercise I suppose to be in a much better shape at the end of the year, when I projected a nine day tournament.
On the other end of the spectrum, I do daily exercises with the nine most frequent occurring mates. I expect to master them too fully at the end of the year.
So I'm closing in on the middlegame from two sides.
There are only two works about the middlegame that I'm aware of that try to dive deeper in the theory behind the middlegame: My System of Nimzowitsch and the Art of Attack in Chess of Vukovic.
My System seems to be gearing around blockading pawns and to encircle and undermine them. Be it in the opening (hypermodern), the middlegame (blockading the center) or the endgame (undermining the pawn blockade and creating a passer).
While The Art of Attack in Chess is dedicated to the attack on the king, especially inspired by both Alekhine and Capablanca.
The Art of Attack in Chess is totally compatible with the PoPLoAFun system. I study the book in order to make the PoPLoAFun system more robust and general. At the same time it becomes clear that the Art of Attack in Chess was a work in progress. It just gives an impetus to the study of the middlegame, but it is by no means finished or complete. So I'm afraid I will have to think for myself again.