Being that they are transformer based they can as a rule accept higher sound pressure levels than the tube condensers microphones. They can be mounted on the inside of the lid on the piano and with the lid closed can produce a workable sound with very little leakage. The next important factor is what type of pattern to use when miking the piano. Many of the microphones I mentioned above have multiple polar patterns. In choosing one you must consider again the type of style of piano, leakage factors and phase cancellation.
Phase cancellation occurs when two microphones are placed in close proximity.
What happens is certain frequencies cancel out making for a lack of those frequencies. When you have two microphones close together under a piano lid and set to undesirable polar patterns the result will be a very unnatural sound. For rock music the microphones have to be as close to where the hammers hit the strings as possible. Cardiod microphones work best. They are more directional.