Just for the record, this has been fixed, and BA and IB charge the same for this route. IB had an IT change which led to some routes being incorrectly allocated to the wrong band, and in this case they used MAD-SIN (7077 miles) instead of LHR-SIN (6765 miles). As a result it ended up briefly in Group 9 rather than Group 8, but that has now been corrected.

BA and IB frequent flyer schemes charge the same amount of Avios for BA and IB services, but IB flights generally require fewer Avios than BA flights for the same distance (there are some exceptions) - and the peak / off peak calendar is different too. IB doesn't have a Reward Flight Saver concept, which BA uses to cap the cash component on shorthaul. For partner airlines the situation gets more complicated - and the partner list is slightly different too - but often Iberia needs more Avios but less cash, the ticket is non flexible on IB, and can only be bought as a return (except Vueling and Level).