Our results use the same £14 total stake per betting day, whether two or three horses qualify.
Why £7 on the Double? It keeps the example budget at £14. The Double puts that money into two lines; the Patent spreads it across 14.
£14 is an example, not a required spend. You can stake less: a £1 each-way Double costs £2 in total. Fewer than two qualifying horses means no bet and £0 staked.