FAA AC91-57 currently 'advises' you voluntarily stay below 400' eveywhere.
ASF400 and g0801 say what happens if you dont fly with in the AC.
AMA used the Infamous 400' Comma to make it an AMA 400'ceiling only when near airports.
The AMA Safety Code clearly states that it is PILOTS that will not bust that Alt without notifying the airport.
http://www.modelaircraft.org/files/105.pdf
2. Model aircraft pilots will:
...
(c) Not fly higher than approximately 400 feet above ground level within three (3) miles of an airport, without notifying the airport operator.
Notice the handy requirement to just 'notify' the airport
arther than saying you have to get the airport to allow you to fly there.
It would be within the letter of the AMA safety code to notify the airport,
and then ignore the airport guys telling you you not to fly there
... after all, you did notify them as required by AMA
and just choose not to voluntarily heed the FAA 400ft 'advice' in the AC, and as some folks will have you believe, therefore ASF400/g0801 dont apply because you are within the AC by exploiting the 'voluntary' nature of the AC restrictions.