On Adire's website, the Tempest in a 194L vented alignment requires two 3" flared ports five inches long. Using Unibox, I plug one port of 3" in diameter, I get five inches. When I plug two ports in, it reads two 3" ports each 12 inches long. Which is right and why? The larger the diameter port, the longer the length required. With two 3" ports, you're basically using a 6" port. When I plug a single 6" port diameter, I get 24" which is the same as using two 3" ports of 12".