Hi
I thought as you, that Kerbin would had a Karman limit lower than 100km....
But I was wrong.....
If Kerbin have : same atmosphere than earth, azote, oxygen, etc.... So the molar mass of air is equal.
If Kerbin have same température......
And if Kerbin have same gravity....
Density and pressure change like on earth so the limit is at the same altitude! Limit depends only these three values calculation