Since Ubuntu 19.04, desktop extensions are not anymore handled by the file manager. Instead, they are handled by a new Gnome Shell extension, "Desktop Icons", which is still very recent and not yet full featured. What you observe is a limitation of how the extension currently works: the extension probably does not (yet) account for the fact that you may want to move the dock to the bottom.
The issue would need to be filed to the developers if that has not been done yet, such that it can be fixed in future versions of the extension.
Since Ubuntu 19.04, desktop extensions are not anymore handled by the file manager. Instead, they are handled by a new Gnome Shell extension, "Desktop Icons", which is still very recent and not yet full featured. What you observe is a limitation of how the extension currently works: the extension probably does not (yet) account for the fact that you may want to move the dock to the bottom.
The issue would need to be filed to the developers if that has not been done yet, such that it can be fixed in future versions of the extension.