how to calculate givendate is before last sunday of the month or after the last sunday of the month

ALTER FUNCTION dbo.fnIsDayAfterLastSunday
(
        @Date DATE
)
RETURNS TABLE
AS
RETURN (
                WITH cteCalendar(theDate)
                AS (
                        SELECT DISTINCT       DATEADD(DAY, f.Delta, d.LastDay)
                        FROM           (
                                                SELECT DATEADD(MONTH, DATEDIFF(MONTH, '18991231', @Date), '18991231')
                                        ) AS d(LastDay)
                        CROSS APPLY    (
                                                SELECT 0 UNION ALL
                                                SELECT -1 UNION ALL
                                                SELECT -2 UNION ALL
                                                SELECT -3 UNION ALL
                                                SELECT -4 UNION ALL
                                                SELECT -5 UNION ALL
                                                SELECT -6
                                        ) AS f(Delta)
                )
                SELECT SIGN(DATEDIFF(DAY, theDate, @Date)) AS Position
                FROM   cteCalendar
                WHERE  DATEDIFF(DAY, '18991231', theDate) % 7 = 0
        )

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N 56°04'39.26"

E 12°55'05.63"