WinISD transfer function magnitude

Sorry to ask something that's already been asked, but I can't find a very precise answer.
Say I have a subwoofer I want to put in an enclosure, and have a flat frequency response down to 40 Hz.

What I get, in "transfer function magnitude" from WinISD, after some tweaks from what WinISD advised me (little bit bigger box, an eq... who knows ?), is a flat transfer function magnitude. Great !
From 40 Hz (-3dB) to very high frequencies, the transfer function magnitude is flat.

What I see here is either :
1 - What the frequency response of my woofer after I put in that box will be
OR
2 - The gain of the box, meaning the free field frequency response of the woofer will remain unchanged from 40 Hz to high frequencies.

I was thinking it would be 1, but now I realise I doesn't make any sense, 2 seems much more logical.

If the correct situation is the situation 2, then I should design this transfer function magnitude trying to correct the free-field frequency of the woofer in order for it to be flat, rather than having a flat transfer function magnitude wich will just not change anything after 40 Hz.

Am I right ?

Thanks !

I was asking about that :
from 150 hz and down, is it 1 or 2 ?

I mean it has to be one of them