Taping cement backerboard (Hardiebacker) at ceiling

In preparing for ceramic tiles, I've installed backerboard on three shower walls to within 1/4" to 1/2" of the existing painted, sheetrock ceiling. The question is, what to do with that gap. Possibilities:
1. Leave the gap empty (think of it as an expansion gap) and simply cover gap with the ceramic tile to within 1/8" or so of the ceiling and caulk there.
2. I could fill it with caulk, then cover it with tiles as described in 1.
3. Treat it like the other joints between backerboards and tape it and cover the tape with the thinset. Will thinset adhere to the painted ceiling? (I'll roughly sand it first to kill the gloss.)
Thanks for you suggestions. Please also email them to me, fixing my address.
Ray
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yes
could be done, but why?

are you planning on tiling the ceiling? if not, then you don't want thinset there.

address.
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