Lt.
Kurt Wissemann (Jasta 3) was shot down by pilots of 56 sqn. on 28 September 1917 in the Thourout-ruddervoorde-Courtrai-menin area. (see "Who Downed the Aces in WW1?) They were in the right location at the right time. I am still checking but Fonk's sqn. did not appear to be in that area.
One has to wonder if Fonck's credibility should be questioned. In "Bloody April...Black September" there was the suggestion in September 1918 Fonck took credit for another pilot's claims when he thought the other fellow had been shot down. A bit of embarresment when the "downed" pilot appeared! Afterall, there has to be more to the negitive feelings most other pilots had for him other then personality.