I fly over water all the time, in Dominican Republic and The Bahamas, but have not really tried distance runs. Download an app called Windfinder, and pay attention to maximum winds and direction in your area. I would try approximations first, fly out until signal gets weak and fly back immediately. Remember wind direction on the way back can really hurt you. Try to go a bit farther out every time. Winds are usually low in the morning and maximize between 2 and 5pm, but this could be tropical patterns and not in your area.