Yes, midhorns have to be fairly long. Their length should be at least 1/4λ of the cutoff frequency. The 9π midbass horn, for example, is 32" long. That will work down to about 100Hz. You can see from the Hornresp model, that's where it starts to roll off.
9
π Midbass Hornresp input screen
9
π Midbass SPL response