Yes you can over power a Tuner. I'll give you an example:
I have 2 DB8 outdoor antennas stacked and mounted 30 feet off the ground. My local towers are less than 10 miles away. Even though the DB8's are considered multidirectional, all antennas have a face. If I face my antenna in the direction of my local towers, the signals are too strong and overload my tuners. Tablo is not to blame here. It happens with with all my TV's (3), my Silicondust HDHomeRun network tuners, and my Tablo.
My antenna is also about 65 miles from a neighboring city's towers. I turned the face towards those towers. Now I pick up the channels from 2 cities and my local towers are now picked up from the back of the antenna which weakens the signals enough so they do not over load the tuner.