I cut out the bottom end cap for my sonosub (18.5"). It looks like I probably won't have room for the 4" flared port since it looks to be 5" diamater in pictures, and the shiva takes up most of the bottom end cap as it is. Is it better for the port to be on the same side as the driver? Should I get a 3" flared port instead? What length would the port need to be if my volume is about 142 liters? Thanks in advance!!