_SCREENMOVE _MIDDLE and resolutions

[NakedApe]

Howdy. I want a program to run at 1600x900 on desktops and 1280x720 or 1280x800 on laptops. That seems straightforward enough, but this sub - at the big resolution so far - doesn't actually center the program window on the desktop. Why is _SCREENMOVE _MIDDLE opening this window far to the right and off-screen? Also any suggestions for improving this resolution changing sub will be gladly and humbly accepted. Thanks! Ted
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SUB resolution () '                     first attempt at resolution changer
    '                                             I want 1600x900 on larger screens else 1280x720 or 1280x800 on smaller
    DIM ratio AS SINGLE
  
    IF _DESKTOPWIDTH > 1750 THEN SWIDTH = 1600 ELSE SWIDTH = 1280
    ratio = _DESKTOPWIDTH / _DESKTOPHEIGHT

    IF ratio = 1.6 THEN '               8:5 aspect ratio - 13" macBook
        SHEIGHT = SWIDTH / ratio
    ELSE SHEIGHT = SWIDTH / 1.777 '     16:9 aspect ratio
    END IF

    CLS
    PRINT "Screen Width is"; SWIDTH
    PRINT "Screen Height is"; SHEIGHT
    PRINT "Aspect Ratio is"; ratio;
    _DELAY 3

    SCREEN _NEWIMAGE(SWIDTH, SHEIGHT, 32)

    IF SWIDTH = 1280 THEN '                     laptop mode in fullscreen
        _FULLSCREEN , _SMOOTH
        IF _FULLSCREEN = 0 THEN '               on fullscreen error
            BEEP: CLS
            _FULLSCREEN _OFF
            PRINT "Fullscreen failed. Going native. Press a key."
            SLEEP
            _SCREENMOVE _MIDDLE
        END IF
    END IF

    IF SWIDTH = 1600 THEN _SCREENMOVE _MIDDLE '        I put this here after the SCREEN statement, but it still doesn't center the program window

    CenterX = SWIDTH / 2 '                define screen center points
    CenterY = SHEIGHT / 2 '
END SUB
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