Didn't mean to frustrate, it's just the wording of the AMA code is a tad ambiguous. Observe:
"5. I will not fly my model aircraft higher than approximately 400 feet above ground level, when within three (3) miles of an airport without notifying the airport operator."

That stupid comma muddles everything up. If it is separating two sentence objects, then it can be separated as follows:
1. I will not fly my model aircraft higher than approximately 400 feet above ground level.
2. I will not fly my model aircraft when within three (3) miles of an airport without notifying the airport operator."

Without the comma, then it means what you say: the altitude limit only applies when near the airport. It gets better: it would mean you CAN fly over 400ft by the airport, but you have to notify them first.

Every sentence will make sense to the person who wrote it. They need to have others proof-read their polices more often.