Sorry, habe mal gelernt, dass der final reserve fuel bei jets für 30min in 1500ft above alternate elevation zu berechnen ist. Hat sich das auf 4000ft geändert?

Es gibt da mehrere Regelquellen -- ICAO, EASA NCO, EASA CAT, etc.

Nach EASA Part CAT

5) Final reserve fuel, which should be:
(i) for aeroplanes with reciprocating engines, fuel to fly for 45 minutes; or
(ii) for aeroplanes with turbine engines, fuel to fly for 30 minutes at holding speed at
1 500 ft (450 m) above aerodrome elevation in standard conditions, calculated with
the estimated mass on arrival at the destination alternate aerodrome or the
destination aerodrome, when no destination alternate aerodrome is required.

Nach NCC.OP.130 und NCO.OP.125 (also GA)

(2) for IFR flights:
(i) when no destination alternate is required, to fly to the aerodrome of intended
landing, and thereafter to fly for at least 45 minutes at normal cruising altitude; or
(ii) when a destination alternate is required, to fly to the aerodrome of intended landing,
to an alternate aerodrome and thereafter to fly for at least 45 minutes at normal
cruising altitude.

Es gibt für GA also zwei entscheidende reichweitenverlängernde Erleichterungen:

1. Man braucht u.U. kein Alternate (wie schon immer unter FAA)
2. Man darf das Holding in der sparsamsten Höhe fliegen