How are the Heat so mid but so good against us?

Heat lost by 9 to the Memphis 3rd stringers. They have now lost 4 in a row to sub 500 teams. How are they objectively a mid team but so good against us and the Bucks? They just hit insane 3s and shots against us that they miss against any other team. And when they get to the Finals where they had no business being they revert back to being the mid team that they are.