Currently, if there are not enough rows to fill the height of RadGridView control, the pinned row will appear right after the last row. It will be good to facilitate customization that sets the pinned row to appear at the bottom of the grid. Same logic holds for summary rows and columns.

Workaround:

public Form1()
{
    InitializeComponent();

    DataTable dt = new DataTable();
    dt.Columns.Add("Id");
    dt.Columns.Add("Name");
    for (int i = 0; i < 5; i++)
    {
        dt.Rows.Add(i, "Item" + i);
    }

    this.radGridView1.DataSource = dt;
    this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;

    this.radGridView1.AllowSearchRow = true;
    this.radGridView1.SearchRowPosition = Telerik.WinControls.UI.SystemRowPosition.Bottom;

    this.radGridView1.ViewDefinition = new CustomTableViewDefition();
}

public class CustomTableViewDefition : TableViewDefinition
{
    public override IRowView CreateViewUIElement(GridViewInfo viewInfo)
    {
        return new CustomTableElement();
    }
}

public class CustomTableElement : GridTableElement
{
    protected override RowsContainerElement CreateViewElement()
    {
        return new CustomRowsContainerElement();
    }
}

public class CustomRowsContainerElement : RowsContainerElement
{
    protected override SizeF ArrangeOverride(SizeF finalSize)
    {
        float y = 0;

        this.TopPinnedRows.Arrange(new RectangleF(0, y, finalSize.Width, this.TopPinnedRows.DesiredSize.Height));
        y += this.TopPinnedRows.DesiredSize.Height + ElementSpacing;

        this.ScrollableRows.Arrange(new RectangleF(0, y, finalSize.Width, this.ScrollableRows.DesiredSize.Height));
        y += this.ScrollableRows.DesiredSize.Height + ElementSpacing;

        this.BottomPinnedRows.Arrange(new RectangleF(0, finalSize.Height - this.BottomPinnedRows.DesiredSize.Height,
            finalSize.Width, this.BottomPinnedRows.DesiredSize.Height));

        return finalSize;
    }
}