I am intrigued and puzzled by a repeated line in Ewan MacColl's stirring version of the incest ballad "Sheath and Knife."

The line is: "The sun gaes tae your tower there with..."

(There was a sister and her brother The sun gaes tae your tower there with Wha maist and tightly loved each other God give we had never been sib...)

Is this merely a homonym, wherein some researcher heard "the son goes to your (her) tower there (to lie) with" (his sister), and made it out as some directional information like "there was a lady in the North"? Or am I missing some other meaning?