I thought Ambush was restricted to 90% in version 1.01 in order to make sure that units could be killed to satisfy the 90% rule.
In a game I am in my single unit was attacked by an enemy Assassin who was 100% guaranteed to win the battle. He won via ambush. When I looked at the battle replay he showed as 108% chance to kill (100% personal + 8% group) when I would have expected 91% or 92% (ambush capped at 90 + his combat chance to win the battle).
KGB