I'm tiling my front room (previously carpeted) and ran into this challenge. The brick fireplace hearth box sits on a concrete foundation that creates a 2-inch wide lip around the hearth. This narrow strip is about 3/8" higher than the wood subfloor. I'll use 1/4" hardibacker on the wood flooring so it will be pretty close to the same height as the concrete, but will clearly never be perfectly level with it.
Any suggestions on how to create a reasonable interface between the tile floor and the last two inches surrounding the hearth box? I suppose I could find a nice bull-nosed edge tile to lay on top of the concrete strip--or chisel away 1/4" off the top of the concrete and try to get it exactly even with the subfloor + backer board (I'm skeptical about this).