Very much so Sedburg!
I think it's something to do with the struts being above the wing that spoils lift much more than struts under the wing? I'm sure somebody with a bit more technical aerodynamics experience could explain it. The poor old T31 is very draggy for a glider, but not to bad for a powered aircraft of its vintage. It's no worse than say a Luton Minor when converted, and with that big wing the loading is light so the engine doesn't need huge amounts of power to keep it airbourne
SS