To move the footnote from the default (lower left corner) position:

ch.Set 'fstyle' 'right'   © right aligned
ch.Set 'fstyle' 'centre'  © centred

The footer is always written along the very bottom of the chart area. Either “Centre” or “Center” is recognised here. Use style ‘Ruled’ to rule across the entire chart area, just above the footer and ‘Pitch=xxx%’ to alter the inter-line spacing.