Beyond that, corner loading of a truncated horn is something I would consider a requirement. But putting a horn in a corner doesn't lower the flare frequency very much, the real benefit to undersized horns is that it smooths response ripples. At very low frequency, the system is pretty much just a direct radiator and in this mode, the driver's excursion and other specs are more important than the horn part of the cabinet. The passages that make up the horn become useless under the flare frequency.