I'm interested in offering reward points and would like to offer the customer more points (say 2p in the pound rather than 1p in the pound) when the sub-total is over a certain amount (say £25.00).

Is this possible/or advisable? Has anyone tried this?

If so, could anyone point me in the right direction for the relevant sub-total functions that would need an amend.

Any help appreciated, and thanks in advance.