It's hard to tell from the pictures, but I'm assuming the bottom plate is recessed, and then there are holes drilled in that to increase surface area? Or are you only getting flow through the connections between holes?
Code:
+---|##|---|##|---|##|---+
|__M|##|MMM|##|MMM|##|M__|
+--\ /--+
| \WWWWWWWWWWWWWWWW/ |
+------------------------+
Side note: Does anyone know how to prevent multiple spaces being condensed into one?