This looks like a bug in the calculation of the max value for a stacked chart.
I can reproduce this with the Northwind orders table:

select *, shipvia * 60 as sv From orders limit 22
GO
.setPivotResultSettings 'Index=1,
    RowFields="[ShipCountry] {None} ASC",
    ColFields="[ShipVia] {None} ASC",
    DataFields="[Freight] {Sum} ASC",
    ShowChart=true,
    ShowToolbar=true,
    Paging=true,
    Split=425,
    Chart="{stacked,stacked,stacked}",
    RotX=325,
    RotY=-13,
    RotZ=0,
    ZoomScalar=1.7499999,
    ShowLegend=true,
    ShowLegendBorder=true,
    ShowGrid=true,
    FillGrid=true,
    GridLineWidth=1.0,
    Title="",
    TitlePosition="Bottom Center",
    TitleCategory="",
    TitleValue="",
    PieExplode=0.0,
    GroupSmallValues=true,
    SmallValuesThreshold=3.0,
    PieLabelDistance=3.0,
    PieShowLines=false,
    LineWidth=1.0,
    ShowMarkers=true,
    MapShowBackground=false,
    MapShowDetails=false,
    MapRange="",
    MapRangeColors="",
    Width=16.0,
    Height=10.0,
    Depth=5.0,
    SeriesSpacing=1.0,
    CategorySpacing=1.0,
    Font=Arial Bold-BOLD-10,
    LegendFontSize=1.0,
    SeriesFontSize=1.0,
    CategoryFontSize=1.0,
    ValueFontSize=1.0,
    TitleFontSize=1.75,
    AxisTitleFontSize=1.25,
    DataLabelFontSize=1.0,
    TopColor=#ebf0f5,
    BottomColor=#d7dcf5,
    PanX=-98.0,
    PanY=93.0,
    Lighting=Default,
    Opacity=1.0,
    View2D=false,
    StackedPercent=false,
    ShowValueAxis=true,
    ShowValueAxisTicks=true,
    ShowValueAxisLines=true,
    ReverseValueAxis=false,
    ShowCategoryAxis=true,
    ShowCategoryAxisTicks=true,
    ShowCategoryAxisLines=true,
    ShowSeriesAxis=true,
    ShowDataLabels=false,
    ValueAxisNumberFormat="",
    CategoryAxisNumberFormat="",
    CategoryAxisDateFormat="",
    CategoryAxisDateTimeFormat="",
    CategoryAxisTimeFormat="",
    SeriesAxisNumberFormat="",
    SeriesAxisDateFormat="",
    SeriesAxisDateTimeFormat="",
    SeriesAxisTimeFormat="",
    NumericCategoryAxis=false,
    MergeAxis=true,
    SeriesAlias="default,default,default",
    SeriesSubType=",,",
    SeriesColumnType="Cube,Cube,Cube",
    SeriesMin="default,default,default",
    SeriesMax="default,default,default",
    SeriesColor="default,default,default",
    SeriesFunctionMetaData="true,true,true",
    ShowSeriesDataLabels="false,false,false",
    LegendPosition=Top Right,
    LegendWidthType=Fit,
    LegendWidth=100,
    LegendHeightType=Fit,
    LegendHeight=160,
    ShowFixedCategoryCount=false,
    FixedCategoryCount=0,
    ShowFields=true,
    ShowTotal=true,
    ShowSubTotal=false'

If the user manually sets the merge series max, then you can workaround it for now.  e.g. here are a few images:
chart_without_max.png shows the default bad behavior (with the max at 600).
chart_with_max.png shows the chart with the max manually set to 400. 
chart_option_dialog.png highlights the property to set