Round,
When level at 200' or thereabouts, tilt control should be set about level which will give about +/- 3 to 5 degrees of scan above and below the horizontal depending on the diameter of the aerial.
"Level" to what would be the Horizon and compensating for Aircraft Pitch Attitude variation of what would otherwise be Wings Level in Pitch due to the speed it is flying? Is that the "Level" to which you refer?