Shortcuts will not work. No asteroids or stars computed to be fainter than this limit will be presented in the plot. As the magnitudes of many asteroids are not well known, you should be aggressive with this parameter, say by adding as much as a magnitude to what you think your telescope can detect. This selection parameter eliminates all asteroids whose probability of imaging is less than the specified value. The probability of imaging depends on your FOV and on the ephemeris uncertainty, expressed in standard deviations, or sigma, of the asteroid.
Sigma is the standard deviation described in all statistics texts.
In the context of asteroid orbits, the position of the asteroid is uncertain because the orbit depends on astrometric measurements that contain errors. Thus, the orbit calculation, almost always a least-squares fit, will reflect some of the measurement errors. Because we know where the LOV crosses your FOV, we can use Gaussian statistics to calculate the probability that you will see the asteroid. Suppose an asteroid with a one-sigma ephemeris uncertainty of one arcmin and a horizontal LOV is just off the FOV in the RA direction. This asteroid will not be selected because it is more likely the asteroid will be off the image than on it.