If your pick ups are too close to the strings, the magnets will affect the oscillation. This will result in a loss of sustain.
If you're new to floating trems, make sure you read the tech section on set-ups. Trem angle is extremely important, make sure that it is done correctly. This can also affect the string height. When adjusting the height, remember to loosen the set screws inside the posts. After getting the action where you want it, it may be necessary to re-intonate.
With floating trems, a good rule of thumb is for every action... there is a reaction.