Right, as you can see on the first illustration,
and on the Wieselberger diagram, the effect starts at about
one span altitude. A high AR wing vortex will probably have
a bigger radius than a low AR wing since the lateral airflow
has a bigger distance to travel from root to tip. So it will get
in conflict with the ground sooner.
The percentage of drag reduction in the two cases will offcourse be the same,
but the F104 will loose drag faster and more than the glider.
M