Keep going at it with a broad bolster / chisel attachment, the sharper the better. You'll never get it perfect though.
Alternatively say fuck it, pour self levelling compound once all the tiles are up and accept that the floor will be ~ 5mm higher than you originally anticipated.
The best thing really is to take the highest spots off then to go for self levelling compound.
Keep going at it with a broad bolster / chisel attachment, the sharper the better. You'll never get it perfect though.
Alternatively say fuck it, pour self levelling compound once all the tiles are up and accept that the floor will be ~ 5mm higher than you originally anticipated.
The best thing really is to take the highest spots off then to go for self levelling compound.