Hi Anibal

You would do a sodium bullet test to visualise the sample flow in the plasma and to check if your sample introduction system is setup properly. The parameter to adjust is the nebuliser gas flow, ensuring Atomisation at the right place of the plasma. I don't think there is a generic distance above RF coil where the bullet should be, but it should extend one or two mm into the plasma, especially if you operate the PE8300 in radial view.

The important parameter to observe is the shape of the bullet it shouldn't be distorted, or fainting.