Thank you all, gentlemen!
I know that mr. Van Mombeek has the Flugbuch of Fritz Haspel (according to his website). Maybe there are more details to be found in that book? I'm convinced that the book covers details that are unknown right now.
Unfortunately no more information exists concerning the crashes of Mattern and Sainisch. The wreck locations and combat history of these pilots on that day are therefore impossible to retrieve...