Sean;
A few suggestions:
1. Should you wall mount the two BL 6000 as rear speakers, consider mounting the pair LOW, and against the wall studs (wood frame ) unless your wall is masonry constructed. Your rear speaker sound should reach you and your audience directly, just over any tables, sofa, or chairs. Mounting the speakers on studs, versus gypsumboard (wallboard) provides better resonance, and more security should something, or someone bump into them accidentally.
As you note, if your speakers are placed too high, you do not receive the full sound as B&O intended for your enjoyment.
2. I have BL 4000 speakers, and have tried the ceiling mounting as rear, and as side sound sources. The Bl 4000 can be angled downwards towards the audience very effectively, using the special ceiling bracket option.
I have seen pairs of BL 4000 successfully placed in two restaurants in this manner. So successfully in fact, that despite the large volume of luncheon and dinner patrons, they had to be zoned down. ( That was my Eagle Scout good deed to the Maitre d' of one of the Hotel-restaurants, who was unfamiliar with the B&O steup features, and felt the speakers were getting too loud in the main dining room. He was correct; They were ).
Again, if you choose this option, mount the speakers on a beam, or ceiling 2nd story floor stud, or something sturdy. You achieve again much better sound and mounting security.
I mentioned above that I tried this second method. I later opted for a change of BL 4000 back as front speakers, and replaced the ceiling Bl 4000 with BL 4 as the rear, and ceiling-mounted set of speakers. This is a better sound mixture of one dominant speaker pair, and one subordinate speaker pair for us.
I hope this is helpful information to you.