MB4 205a: Throwing from a Domain Through Another Domain on Shabbos (353:1-2)

If two houses separated by reshut harabim owned by one person then throwing items between the two is permissible if they are at the same elevation since it might fall in between and you may come to carry it.

What if there is a karmelit and not a reshut harabim in between?

The status of a ledge that projects from a house into reshut harabim.