Its well known (usually) that most times rear-firing will give a big bump in the lowest octaves due to wave reinforcement, and a semi-bandpass effect in trunk vehicles. Facing the subs forward and sealing off the trunk does lower the amount of airspace to compress, but it also greatly affects freq response, and freq response is a big factor in how loud a system sounds 'to the human ear'. If you were to RTA your system before and after the change, you will probably notice less output in the lowest octaves, but an over all more linear freq response.
If you flipped your subs forward and sealed off the trunk for SQ reasons, you succeeded. But if you did it just to increase output, you screwed up.