I'm running into this issue now. Kelkemello dies every single time I try. I can manage to make him survive with a slowfall spell, but that just breaks the duel script instead of triggering him to forfeit. Nothing else seems to be working, he just dies as soon as he hits the ground. Can't even use console commands to get past it, as trying to set a journal stage just gets all three stuck out there in the courtyard, and I've not been able to find one that lets Kelkemello survive the fall AND advance the quest.

Generally it feels like the modified spell just throws Kelkemello too high up (he goes basically to the first balcony of the Great Hall?)... are there any modifiers for it that determines how high he's thrown, or something?