That's fair enough, I think I'm 1 of 3 people in this topic who has first hand experience regarding these!
I have personally seen jacks forks, personally seen both Coust bros forks and spoke to there dad about the mod he's made to them
Fact if you run a king headset with your frame which has a 105mm headtube length the stack height will be 136mm +\- .10mm I know this because I measured it myself!
Yea this is a guess not a fact, if you make an insert it will void the warranty, but jack don't have to worry as he's sponsored by koxx