If your board has plugs for you to place your footstraps further inside, away from the rails, you might want to try that if you're new to slalom sailing to enjoy a comfortable stance and good control. Consider this an option too for more hard-core conditions.
TAKEAWAYS:
Straps Forward - Prevents Tail walking/too much lift
Straps back - generates lift
Tall Riders - use wider stance with extreme back and front positions
Shorter Riders - Use front strap's front position and narrower overall stance.
Outside rail positions for power and speed - good for advanced riders and easier conditions
Inside positions for control and comfort - good for less experienced sailors and difficult conditions.
Start with everything in 'neutral' and recommended settings and work your way from there. Confirm any improvements by testing against friends or a GPS, as sometimes it's hard to tell from feel alone.