Tractix horns according to Dr Bruce Edgar(and others also) are shorter than other horn designs(hyperbolic/exponential/etc).
Tractix horns also are not designed to be used to their flare frequency since at the end of the flare(mouth) ends up being 90 degrees referenced to the throat.
Simple examples:
Edgar round tractix horns:
650hz flare - designed to be used no lower than 800hz minimum
500hz flare - designed to be used no lower than 800hz minimum
350hz flare - designed to be used no lower than 500hz minimum
While the 650hz flare works to 800hz(not well enough for my ears), I found a better overall sound performance when crossed over at 1khz or higher.
Not trying to confuse things here, just giving my points of view in the hope that it might help out.
Ron