The Mechaber says (Shulchan Aruch Orach Chaim 671:4) that the Chanukah lights may not look like a bonfire. The Remah therefore says that the Chanukah lights must be in a straight line, to make sure it doesn't look like a bonfire. The Mishna Berura (SK 16) says that the candles can't even be staggered (one in and one out), so that one doesn't come to set them up in a circle.
Do the candles have to be set up in a perfectly straight line, or are slight variances acceptable (sources please)? If slight variances are acceptable, how much?
Does this idea of the candles being in a straight line also apply to up and down, or just side to side?