Before attributing an epicanthic fold to a 12th century ancestor, it would be helpful to read the posts in the thread Autosomal Analysis Question.
On average, any one ancestor’s contribution to your DNA is halved for every generation further back from you that ancestor is. An ancestor living in the 12th century, on average, would be expected to contribute about one billionth or less of your DNA. Endogamy could result in more DNA than that making its way to you, but quantifying it is impossible.
On balance it would be far more plausible to find a recent Asian ancestor to explain the introgression of genes for the epicanthic fold into your lineage than one 12th century ancestor.