I am not sure I undertand you correctly but it simply does not matter what driver you use. To do anything really significant as far as directivity is concerned you will have to use a tweeter with these older style horns. They use their directivity to compensate for the compression drivers natural rolloff to give you reasonably flat on axis response. The DI of the horn cannot be changed or compensated for.As Ian surmised, I was thinking of the older style horns, my 511b’s, which have a reputation for beaming in the higher frequencies. I can only expect that to increase when I try to augment their HF performance with the BMS drivers.
Rob