You might try not shocking the line with a crisp stop when the line straightens on the back cast. That's perfect for dries but with big, air resistant flies it might cause a shock wave in the line which could cause slack which ain't very efficient.
Besides opening yourloops, try to cast in slight ovals... lower on the back casyt than the forward cast.
Note there are a lot of 'mights' and coulds'.... JC is watching and if anyone can keep us honest with casting it's him!