OK, riddle me this: We're 9th overall in FG% allowed (.459), and we're also 9th overall in 2PT% allowed (.528), but we're **29th** overall in 3PT% allowed (.377)! Teams just take so few 2PTers against us (27th in the league) and so many threes (4th) that the fact that 3PT percentages are lower in general evens things out on FG%.
To show how meaningless FG% allowed is, we are 19th in eFG% allowed (.545). (BBRef does not have opponent TS% but presumably it is similar.) It would appear that it's the fact that we're pretty good at forcing turnovers (11th) and defensive rebounding% (5th) that brings our DRTG up to 13th.