Miles M I agree, but It should perhaps be emphasised that whilst the AMC provides a method of compliance, the three-tier system is not a fixed requirement from which no deviation is allowed, as some seem to think - the operator may (and indeed ought to) decide what criteria are pertinent, and how they might be categorised or treated, given their equipment and level of experience in conducting the given operation both from the standpoint of crewing and oversight. As any chosen solution requires the permission of the Authority, anything less involved than what is in the AMC is not likely to see the light of day - follow the AMC and you'll be legal but really, a lot more thought ought to go into the task.
For reference, the regulation itself makes no mention whatsoever of airfield categories, it simply requires an operator to ensure the PIC/Commander has "adequate knowledge":
ORO.FC.105 Designation as pilot-in-command/commander(a) In accordance with 8.e of Annex IV to Regulation (EC) No 216/2008, one pilot amongst the flight crew, qualified as pilot-in-command in accordance with Annex I (Part-FCL) to Regulation (EU) No 1178/2011, shall be designated by the operator as pilot-in-command or, for commercial air transport operations, as commander.
(1) the minimum level of experience specified in the operations manual;
(2) adequate knowledge of the route or area to be flown and of the aerodromes, including alternate aerodromes, facilities and procedures to be used;
(3) in the case of multi-crew operations, completed an operator's command course if upgrading from co-pilot to pilot-in-command/commander.
(b) The operator shall only designate a flight crew member to act as pilot-in-command/commander if he/she has:
(1) the minimum level of experience specified in the operations manual;
(2) adequate knowledge of the route or area to be flown and of the aerodromes, including alternate aerodromes, facilities and procedures to be used;
(3) in the case of multi-crew operations, completed an operator's command course if upgrading from co-pilot to pilot-in-command/commander.
(c) In the case of commercial operations of aeroplanes and helicopters, the pilot-in-command/commander or the pilot, to whom the conduct of the flight may be delegated, shall have had initial familiarisation training of the route or area to be flown and of the aerodromes, facilities and procedures to be used. This route/area and aerodrome knowledge shall be maintained by operating at least once on the route or area or to the aerodrome within a 12-month period.
(...etc.)