I have several HBD12s, used them for "budget" events, where both coverage & throw tend to be more than adequate, but my first experience of outdoor horns was big EV (very) rectangular horns, where vertical mounting gave a noticeably wider spread.
Returning to topic - it sounds like you have plenty of scope to mount speakers where you want, Richard, so a centre-cluster is probably your best bet.
Re Jon's last post - for my last 2 church jobs I retained the existing pair of Philips columns, which were still fine, & added a couple of full-range speakers below them for music. Stereo in both cases, but maybe I should have stuck to mono?