Zevahim 40: The Curtains and the Incense

In light of the placement of blood on the inner altar - either one or two placements - preserving the atonement capacity of the offering, even without blood placed on all four corners, the question of blood on the curtain (parokhet) must be asked. The Gemara establishes that all seven placements must be made on the curtain - but it asks also about four placements, because of a verse with a plural term and R. Shimon's opinion. Also, why does the Torah specify the need for incense on the inner altar (which was the incense altar), as the terms are redundant? Plus, the focus on the verses as source material for the halakhic details.