Using this snippet to modify the PageHeader section of a PDF report, I have no spacing issue

protected void WebGrid1_PrepareExportExecute(object sender, PrepareExportExecuteEventArgs e)
{
    ActiveReport3 report = e.ReportObject;
    DataDynamics.ActiveReports.Label lblProject = new DataDynamics.ActiveReports.Label();
    lblProject.Text = "Report Custom Header";
    lblProject.Alignment = TextAlignment.Left;
    report.Sections["PageHeader"].Controls.Add(lblProject);
}

You could use the Custom AggegrateFunction property. This way you could handle the aggegrate function and return the total value that will comply with your scenario. The event handler will be handled by CustomAggegrate server side event. Here is the snippet:

protected void WebGrid1_CustomAggregate(object sender, ISNet.WebUI.WebGrid.CustomAggregateArgs e)
{
    if (e.Column.Name == [ColumnName])
    {
        //Get the GroupTotal using custom function
        e.AggregateResult = GetTotal();
    }
}

Issue discussion is continued on this thread

In a ClientBindind scenario, please use ClientBindingSettings ServiceEvents Selecting to add custom filter. This way the filter argument will be used during the data selecting (Paging will be taken into account)

Using the ClientBinding_Paging.aspx sample, add ServiceEvents Selecting. WebGrid Definition:

<ClientBindingSettings DataLoadMode="PagedData" DataSourceType="WebService" ItemTypeName="Bug"
    ServiceUrl="WebService.asmx">
    <ServiceMethods BatchUpdateMethod="UpdateBugs" SelectMethod="GetPagedBugs" />
    <ServiceEvents Selecting="WebGrid1_DataSelecting" />
</ClientBindingSettings>

 Here is the event handler snippet, all filter action will filter the data which has Target value similar to fut or bug:

function WebGrid1_DataSelecting(gridObj, selectArgs) {
    if (selectArgs.FilterExpression != "")
        selectArgs.FilterExpression = "[Target] like 'fut' or [Target] like 'bug'";
}