That's a very good point about the overall dimensions being the same except for the height. My thought was that the decreased height would allow me to place one or both of the speakers on the media center, or another piece of furniture in the room, which would give me more placement options. The lack of a passive radiator on the Heresy might also make effective placement a bit easier. I also think the Heresy is generally a bit more attractive than the Forte, and so the WAF might be a bit higher.
I hesitate to suggest this on a Klipsch forum, but if you're right about the dimensions, maybe I'd be better off looking for another vintage speaker with similar mid / top characteristics, but in a smaller cabinet and (i guess) lower efficiency. Before the Fortes, I'd run some homebuilt Dayton III MTM's with 89 dB sensitivity, and the volume level was acceptable. I dunno, though, I like the history of Klipsch and the coolness factor of the horns. I don't know how much luck I'd have with matching the characteristics, either. Perhaps a Klipsch is a Klipsch and that's it.