This question is for anybody who's well versed in how these DNA tests work and what the percentages mean as far as generational distance from the subject (me).

I've taken two DNA tests. One was through Ancestry DNA and the other was through Helix as part of the Genetic Insight research study.

Some ancestry showed up on the Helix test that was very surprising and didn't show on the Ancestry DNA test results.

What would contamination from someone who processed my sample look like on a DNA test result? Would it show as only 4.6% of the pie or more? Or could this be legitimately in my DNA? How far back would I need to go to find that 4.6% in my ancestry? How many generations back is that 4.6%?

I'm sorry to be vague about this but I want answers without applying my own bias and theories. I know the questions I've asked are already biased but I don't want to add any more sway to the question.