Ok When tiling an archway and a recessed archway as this one is you need to begin tiling on the inside wall face of the arch and work your way out to the soilder cuts around the inside curve then mark out and place your trim on the outside face and tile around the curve. Archways are a case of tiling the reveal first then trim the outer wall and tile. The exact opposite as one would tile around a square window. A square window you would tile the outer wall cut your trim then fix your reveal tiles. A trim placed on the inside of an archway reveal will distort and apply pressure to your soilder tiles causing them to dislodge at a later date.
To fix this problem the
tiler will need to cut his/hers soilder course on the inside reveal glue them around the curve all the way to the floor as this would hide the misalligned tile heights from the back of the arch to the front facing wall, allow to set. Then the easiest way to tidy up the badly cut arch curve is to apply a trim to the outside face edging the soilder course then cut keystone tiles around the trim and glue them on top of the exsisting tiles around the curve and down to the floor creating a 3D type look or "Chunky" style (Not Ideal) but the look would be pleasing.
Not much you can do with the misaliged tile in the top right corner of the pic though.
Heres a couple of pics to follow what i've tried to explain hope it helps
