I just found an article written by Busemann self about this issue!!!!! He says the biggest problem is overemphasize on air technique, most of all on the hitch kick, wich he founds totally detrimental if you aren’t jumping 8m +.
https://www.wlv-sport.de/filerepository/hECTaUNZYVq9e5GNSyC3.pdf
https://www.wlv-sport.de/filerepository/cqUezubkTn6G63mb4kzB.pdf