Well females are the ones with girth. So just get a male. From what I've gathered, if you feed them normally, then you should end up in the target area you want. Maybe Cody will chime in here or check youtube for reptileexperts videos. He gives good advice on what to expect etc etc. While there is no guarantee on the size of any snake, by feeding normally and starting with a high % of SD blood, you will at least have a better chance of a smaller snake.
Kris told me the parents for my guy were 5' dad and 8-9' mom. So my guy should top out around 5-7' with normal feedings. And again, no one can guarantee any size but you can get a general idea. Just have to be prepared for something bigger lol. That's why I went with a male myself. All my reptiles are females and while I did want a female SD/D retic, I didn't want to chance it so I got the male.