Local Rule 16 Explanation

Explanation

The whole bunker is deemed to be Ground Under Repair so for all intents and purposes, the bunker does not exist. 

That is why  ‘16.1b Relief for Ball in General Area’ rather than ‘16.1c Relief for Your Ball in Bunker’ applies. 

(You can click the rule names above to read the official explanations).

The point of entry, just outside the bunker, becomes the reference point.