Average contribution to the proximity of the transmitter

This antenna replaces an antenna August DTA102 which was not satisfactory despite a transmitter located about 750 m from the house.
Connected to a HDS1.1 Metronic in the office of my wife, he succeeded in scan chains in automatic mode, find all channels but reception levels revolve around 18-35% at best by orienting the antenna (the position being horizontal on the top window pane with the suction cup system).
To recall, the transmitter is in "direct line" as seen in the distance (about 750 m from the house) and it is only the thickness of a double glazing that separates them.
Nevertheless, beyond the strength of signals "weak" received, the Metronic HDS1.1 mentions image quality oscillating between 68% and 97% over the wholes chains and no images on the screen type "stutter "or type" mosaic "therefore correct quality except sometimes in the evening according to selected channels with some choppiness (the sound is not jerky) that may be due to the closed wooden shutters and / or at a lower wave propagation the night.