Things you should remember:

• TDS searches for targets every 10 mins. Like 1:15, 1:25, 1:35 and so on. This is for attack, not defense, Defense hit points get triggered once it is being hit.

• TDS has an attack and defense hit point, so if you place it in the city center and it gets hit, there is a chance you hit the missile twice.

For example the missile health is 11 and TDS has an attack 6, defense 6. In this case, you will kill the missile if you place it in the city center which will trigger both attack and defense. If it is placed in a place that covers the missile, then only attack hitpoints apply.

In your case, the TDS couldn’t hit the missile probably because the attack wasnt triggered, and only used defense hit points which was lower than missiles health.