Tifa, Martial Artist and additional combat phases

As I’m reading the text of [[Tifa, Martial Artist]], I interpret the triggered ability as being the untapping ability while the additional combat is guaranteed to happen regardless of whether the power 7 condition is met.

Whenever one or more creatures you control with power 7 or greater deal combat damage to a player, untap all creatures you control. If it's the first combat phase of your turn, there is an additional combat phase after this phase.

The “whenever” sentence lays out the condition to untap. However, the “if” sentence is a new sentence and not explicitly tied to the “whenever” trigger. Reading the card does not explain the card here because every discussion I see about this one appears to implicitly only apply the additional combat if the power 7 condition is met. For example, I have read multiple comments about triggering multiple additional combat phases when by attacking multiple players with power 7s.

What rule applies here that only allows the additional combat to occur if a creature with power 7+ deals combat damage to a player? I was always under the impression that new sentences are evaluated independently, but I have a feeling that I am wrong.