I just purchased Bikilas a couple of weeks ago (my first pair of VFF!) and I had a similar issue. The instep felt just a little too tight, so I tried one size larger in the Women's, but they were too big. I then tried on a pair of the Men's shoes in the comparable size as the original pair I tried on, and they fit perfectly! I am bummed that I don't have a pair of snazzy pink and orange Bikilas, but the blue and grey ones are almost as nice
Good for you, it is not always as easy to find such a perfect fit.