Aero will never be 100% accurate. Especially for PvP combat due to split damage rule and leadership penalty (which it tries to account for). That said, you have 1.4 for "D.Life Base Modifier" (which is default setting). Does the defender have a 5 or 6 star set? My guess is they don't. For 9 star set, enter 2. For 12 star set, enter 2.5. This can make a big difference.

Defender might've also had Art of War and Corselet on. You have to account for all these things if you want more accurate results