How much extra do you need? Enough that a pilot/crew doing their job properly will never run out of fuel and crash.

So yes they will do an "investigation". It's not a criminal investigation. It's to understand the circumstances, the choices, the procedures, and the execution that ended with a plane dangerously close to running out of fuel.

This will determine if there were mistakes made, or the reserve formula needs to be adjusted, or both.

Don't tell me about cost, just stop. Let MAGA-Air accept some plane deaths to have cheap fares.