What is the recommended practice regarding the number of cleansing stones used when exceeding three?

Primary text

If the number of stones exceeds three, it is recommended that the count remain odd, such as five, seven, or nine, based on the command: "Whoever performs Istijmar, let him use an odd number." However, if one stops at an even number of purifying stones beyond three, it is permissible based on the statement: "And whoever does not, there is no blame upon him."