Actually, you need to handle InitializePrint and InitializePrintPreview for the grid.

        private void PosGrid_InitializePrint(object sender, CancelablePrintEventArgs e)
        {
            FormatGridForPrinting(e.PrintLayout);
        }

        private void PosGrid_InitializePrintPreview(object sender, CancelablePrintPreviewEventArgs e)
        {
            FormatGridForPrinting(e.PrintLayout);
        }

        private void FormatGridForPrinting(UltraGridLayout e)
        {
            e.Appearance.FontData.SizeInPoints = 10;
        }

You may also have to re-adjust your column widths if you increase the font size.

Cheers

Allan