Slitherine

playing a couple of times, i found that generally the unit which ambushed the enemy would be damaged more than the enemy, is it a bug???

Well i think ambush situation is giving the defender quite a nice bonus but still if a very weak unit happens to ambush a very strong one, think for an extreme example a transport truck vs a king tiger, it still does not help them enough.

Ambush affects two stats. Attacker initiative is reduced to 0, but this happens before experience and dice roll modifier. So a unit that runs into an ambush can still fire first.
For combat stats, the only stat that ambush affects is the ambushing unit gains +4 defense.

So all in all, Ambush basically means the defending units shoots first (most of the time) and has a better chance at taking less damage.

The results where the ambushing unit is worse off than the ambushed unit, well that's just dice and RNG I guess.

Thanks for the detailed replying