The physical pivot points of the thrust levers are not necessarily where the position sensors (Thrust Resolvers) are located. Often there are rods/linkages attached to the thrust lever mechanisms which drive the position sensors. Due to the geometry of these linkages, the rotary motion of the thrust levers may not precisely correspond to the rotary motion of the position sensors. There may not necessarily be a linear relationship (aircraft dependent).
Of course, the engine control system is programmed to interpret TRA as required.
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