Purity: Position of the Person Praying Relative to the Corpse's Elevation
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 587:
The place where one performs the prayers must not be higher or lower than the corpse; however, being a little higher or lower is not a problem. The recommended precaution is that the place where the prayers are being performed should not be usurped.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)