2 things-
1) It takes a LOT of energy for your body to digest, and absorb protein
2) You can only absorb so much, in one sitting. Much of which is dependent on what your body NEEDS at that time.
IMO- Working out wile on a stomach full of protein is fighting your body for energy usage. Also with the length of time it takes to get digested and into your system, I say 2 hours before is great. By then it will be ready for your body to use. Also remember your body does not use protein for energy synthesis, just to rebuild tissue than wont need to be rebuilt until a time after you make fresh tears int he tissue.
Carbs are absorbed quickly, and are easily digested-and used DIRECTLY for energy-hence why they should be the main part of your pre-workout. Just try to cut the protein down in your pre workout meal/shake-load up on carbs, and quick carbs like sugar, and see if you have a gain in explosive power in the gym.