IB315 Cutout Question

[deftflux 0]

I've tried searching for this, but to no avail, so here's my question: I am planning to mount an IB315 to the rear deck shelf in my car, but not in the usual drop-in fashion where you screw it in from the top.  It will be mounted with the front of the woofer touching the wood baffle and screwed in from behind the woofer.  (Maybe there's a term for this, but it eludes me.)  What diameter should the cutout be?

 

The specs say 14.125" for the cut inner diameter, but I assume this is when mounting it normally.  I am mounting it this way to leave room for the excursion so that the woofer won't touch the speaker grille cloth.  I am trying to make as many modifications to my car as I can while I wait for the woofer (which I ordered a month ago now).  But if I make the cutout and carpet the baffle and it turns out that the opening needs to be bigger, it would be a lot of extra work to do it then.

 

So if someone from Fi could confirm this or if someone who owns one could measure the diameter from the outer edges of the cone surround, I would really appreciate it.  Thanks!!