To specify the width of the Excel-style Customization Form, use the CustomizationExcelWindowWidth property.
To specify the width and height of the Customization Form painted in the Simple style, use the CustomizationWindowHeight and CustomizationWindowWidth properties, respectively.
Use the DevExpress.XtraPivotGrid.PivotGridOptionsCustomization.CustomizationFormStyle property, to specify the style of the Customization Form.