I think 1.0 corresponds to one-half pi radians (90 degrees) when the move object type is angular, and corresponds to the Y-size (or X or Z) of the main body of the entity when in linear mode, meaning setting it to 1.0 will move the object along its axis a number of units equal to the size of the main body along that same axis. Could be wrong though; I don't work very much with move objects.
Also, if you want to move it precisely, just experiment until you find the perfect amount, and declare a constant global variable with that value. Then, instead of moving your object to 1.0 or some other value, set it to 1.0 * PRECISE_MEASURE, where PRECISE_MEASURE is the true "OpenValue" and 1.0 changes based on how far "open" you want your object. Simple little workaround, but it may accomplish what you want without exhaustive testing and tweaking on the entity's properties. Well actually, it'll save you the tweaking. You'll still have to test it