Force facet_cols plots to have identical x-axis?

I like using facet_col with facet_col_wrap=1, because then the labels are above the plots. When I use facet_row the labels are on the side, causing problems with longer labels. Though, in the first case the plots are not build with identical x-axes, because it it facet_cols.

Is it possible to force identical x-axes for facet_cols and/or force the labels to be on top o the subplots when using facet_row?

UPDATE: The problem occurs with both facet col and facet row!!! So, the resulting plots x-axes cannot reliably linked.

newplot (19)|154x500

In that case, how do we know which plots are belonging to the x-axis shown in the bottom plot?

I tried


Which did not help.