If you actually meant "fill", as your post stated, the best place for fill is on-axis. Meaning, right in the hotshoe. And no,I am NOT kidding; fill light works splendidly when it is very close to the lens axis, With a single speedlight in sunny conditions, the sun is the brighter light source of the two; ergo, the role of the flash will be as fill. And fill light works best close to the lens axis. So....stick it in the hotshoe, and aim it at the people. If you look around the Strobist web site, you will find a column David Hobby devoted to how to use on-axis, on-camera flash as fill light. The sun, or the sky, or a combo of those two things, is where the MAIN light will be coming from.
For example: use the light from the sky as the main light for a group. Allow the SUN rays to strike them from behind and off to one side--that will act as a crisp RIM-light. Then, use flash as fill--where it ought to be...as close to the lens axis as possible...in the hotshoe.