Re: Casting in no wind.
OK, I think we need a little clarity on what your cast is like when there is no wind. Does it fall short and loose, or do you have tailing loops? How far are you casting on average? What weight of line do you use (I presume something like 7wt or more if you are casting for distance)?
One thing about wind - it will provide more distance when the stroke is with the wind, and knock down a cast against the wind. If you are casting into the wind most of the time, I expect your forward stroke is too hard for no-wind. But as well, there is no wind to straighten your backcast and help with the load of the rod (and also make that happen sooner than with no wind). I wonder if your backcast is not forceful enough (most aren't) and if you are not allowing enough time for the backcast to straighten when you are casting in the calm.
I sure would like to see a video of your cast, but perhaps you could tell us more.