They might be a little louder, but... even though they are somewhat directional horizontally, there would still be unwanted near reflections from the door windows because they would be on the same plain and closer.
But... if you could make sound absorbers for the ends to block some of the sound from hitting the door windows, and perhaps aim them right.... it would solve the problem of the steering wheel being in front of the driver's side horn when mounted under dash. Interesting. how would you make it look good though?
Going active with horns is probably going to be a must... it's easier to match output levels to the mid-bass speakers using the gain on separate amp channels.