Lots of possibilities if you have time, and viewing stopped-down under a darkcloth also helps to see where the highlights will be. For example, stop all the way down, then open up till you see your hair light, then see if one more stop brings up the face, moving the reflector in. If you have the time.

However, for simplicity, consider also using the sun as the main light, but eclipsed with a hoop of any white diffusion fabric held aloft by an assistant or stand. Sun will be softened, sitter will be comfortable and won't squint, and it will look very natural and pleasing; and when moved in close, you won't need to fill. I used to use fabric held to a hoola-hoop with clothespins.