You do not list the model of your case, but I assume that only the PSU is sucking air from the bottom of the case. From an air-movement point of view, tall feet on the case like you have will allow enough airflow.
Note, though, that some polyester carpets generate excessive static electricity. If your case is metal, you should be fine when the case is closed, but I would avoid handling static-sensitive components (like RAM, or the CPU), while my feet were on such a carpet.