Is correct due to Maneuvering Flaps and Slats that the real plane has according to natops, but we have simplified it for MSFS:
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The real aircraft has 3 flaps positions and 3 slats position: 0, 10, 35 for flaps and 0,7,15 for slats. As you have noticed in game you have 4 levels and not 3. That extra level is 5 for flaps and 3 for slats as part of the maneuvering system.
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The maneuvering system can swap flaps/slats position automatically depending on Mach and AOA and its function as you know is to provide lift at subsonic speeds and prevent stalls at higher AOA maneuvers. That means that the flaps and slats may vary between the 0-2 positions at subsonic speeds when required within a region:
Due to variable sweep wings there are interlocks to prevent flaps and slats damaging the fuselage when wings are sweep, due to that, if you are in manual sweep they will remain in the up position. In the same way, you will not be able to deploy full flaps if the wings are not in the 20 degree position and/or above 265 knots.