If you want to fly a little less (also less TPs and Avios of course) you can substitute EZE by SXM in this example and return to LHR for £1251 or start in LHR and end in MAD and last but not least for £1430 you can start and finish in LHR. Simply see it as flying home via SXM and MIA. All other flights are direct. Also no need for overnight stays in SXM or MIA.