LayoutPanel百分比，它实际上是什么意思？

Question

我有一个分为20行的布局面板，所有行均匀分布相同的大小。 20行@ 5％= 100％但最后一行大约是所有其他行的2倍。为什么会这样？

   // LayoutPanel1
    // 
    this.LayoutPanel1.ColumnCount = 1;
    this.LayoutPanel1.ColumnStyles.Add(new System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Percent, 100F));
    this.LayoutPanel1.Dock = System.Windows.Forms.DockStyle.Fill;
    this.LayoutPanel1.Location = new System.Drawing.Point(4, 4);
    this.LayoutPanel1.Margin = new System.Windows.Forms.Padding(4);
    this.LayoutPanel1.Name = "LayoutPanel1";
    this.LayoutPanel1.RowCount = 20;
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 5F));
    this.LayoutPanel1.Size = new System.Drawing.Size(150, 433);
    this.LayoutPanel1.TabIndex = 4;