Do the recommended changes by adding the 45s and moving the mounting location, in addition, I suggest opening the port up a little bit, it will allow the length to extend further but it will eat up air space so you will have to compensate for that. It looks like you are running 2 12s, you only have 43.75sq in of port area assuming the box is 14in high outside. Thats kind of a small opening for 12s, try bumping it up to around 60sq in, or 5in wide instead of 3.5