Might smaller be louder?

[brendyn74 0]

I am looking into buying the 15 or 18. I would like to say that I would rather get the 18, but that's not true. I want to get whatever will promote the best response with my trunk size. I have a 03 grand prix, and the height of the trunk is only 17 inches. The maximum dimensions the box width and length can be are 35 x 30. My main question is if the surround of the sub is only 1 1/2 to 2 inches away from the lid, will that decrease my response? With the 18 the dimensions would be 15 tall x 35 wide x 29 deep with the port firing into the cab tuned at 33hz.

Will smaller actually give me the most bass? I'm not worried about SQ, just spl...

Thanks in advance! Any help and advice would be great