1)
Why does the Torah call the goats-hair curtains a cover over the Mishkan, and not the bottom curtains?
1.
Rashi (in Yechezkel) and Seforno: Because the bottom set of curtains (the Mishkan) was not made as a cover, but to enhance the looks of the Mishkan by way of the beautiful colored fabrics - Rashi (or so that the Keruvim that were woven into it should surround the Throne - the Aron, the Shulchan and the Menorah - Seforno), whereas the goats-hair curtains were made to cover the Mishkan.
2.
Rashi: Because the bottom curtains themselves are called 'Mishkan'. 1
