I used a fobus for a long time. Initially it was too tight. I heated with a hair drier and boiling water and it helped a lot. In retrospect I don't know why as Fobus is not Kydex, but it did.
If you snap the pistol straight up it helps too. Towards the end, I took a piece of paper and wedged it between the halves at the trigger guard to force them apart a touch (still plenty of retention) and it got better.
I've since moved on to better quality kydex holsters for all my stuff. You can make fobus better, but they are still slower on the draw than Kydex from the better makers IMHO.
HTH,
-K