TileScaleY

public float TileScaleY { get; set; }

[C#]
using (Presentation presentation = new Presentation("demo.pptx"))
{
    ISlide slide = presentation.Slides[0];

    // 获取形状的图片填充格式
    IPictureFillFormat pictureFillFormat = slide.Shapes[0].FillFormat.PictureFillFormat;

    // 将图片填充模式设置为平铺
    pictureFillFormat.PictureFillMode = PictureFillMode.Tile;

    // 将纹理的垂直缩放比例设置为120%
    pictureFillFormat.TileScaleY = 120;
}