Why does the position of the parent comet have no effect on the date of the shower?

The three meteor shower in question happen the same time annually. Why does the position of the parent comet have no effect on the date of the showers?Why does the position of the parent comet have no effect on the date of the shower?
that is because they leave a trail of debris spread throughout the orbital path. So whether it is close or far far away the debris is stille out there. As the Earth orbits the sun it passes through the comets debris field on specific days of the year thus receiving the shower.Why does the position of the parent comet have no effect on the date of the shower?
meteors come from other sources beside comets. the 'radient' is the apparent source of the shower, however, lets use leonids for example, the showers only seem to come from this area and the area itself should only be used as a point of reference i.e. where to start looking
magnetic pull, vs the quadrant the parent basis is recoded in, makes the apparent timing the same every year, even though it in reality is not. hit the books!!