Remember, loquillo, MIA - MAD is a very popular flight - especially since there is a goodly number of flights (IB and IB codeshares) that use MIA as an all-Americas hub. I understand MIA - MAD is one of the more popular award requests, and most pax think linearly of award flights - ergo, Miami. One of the difficulties with the Castellanos broadcasting their language so far and wide

As far as award flights generally, I've always had good luck - planning some time in advance, and being as flexible as I can. And of course, it's always been easier when it's been one pax...

Good luck in your quest.