If you click on the box that shows the Area and percentage (on the left side of the page), it will expand and show you what the range is.

Your 17% could actually have the range of 1% to say 25% (And your Dad may be in the 1% to 20% range)... also if you click on each of the Ethnicity boxes, a more detailed map will come up on the right side ... you could have a parent who shows Irish and/or Western Europe and you could show British. If you look at the individual maps for each of these, you'll see that they overlap and cover some of the same area.

Also read the stories under the individual maps ... that explains why areas of ethnicity may overlap (i.e. why you see Scandinavian in British folks)