As for the placement of the port, it really matters more in larger cabinets where standing waves come into play. The whole thing with the port of a bass-reflex box is that you want bass to enter, but not midrange. You also don't want the port to be in a position where standing waves are at a high pressure node of any bass frequency. That way the Helmholtz frequency is the only significant mechanism in play. Spacing the port as shown in the PiAlign document generally does a pretty good job of that.