No double distance. If you sit equidistant from the two (one sub in front and one behind) then you should enter that distance (from you to one of the subs) in your pre/pro. Also make sure the subs are in phase. This will ensure that sound from your sub arrives in phase with that from your main speakers (assuming you put the correct distance into your mains on the pre/pro)
Finally without performing actual measurements with a microphone and a sweep I don't think you can even begin to know what the actual sound is like at the listening position. If it sounds better by putting in the wrong distance then you have room modal issues or placement issues of a sub is wired out of phase.
Finally without performing actual measurements with a microphone and a sweep I don't think you can even begin to know what the actual sound is like at the listening position. If it sounds better by putting in the wrong distance then you have room modal issues or placement issues of a sub is wired out of phase.