^that's not really how it works, although some companies would love to make it sound that easy.
Adjusting your forward lean (what those pieces do) is primarily & correctly done based on your ankle's range of motion.  If you have a limited range of motion, you do not want your cuff set further ahead of where your limit is.  This would lead to a lot of heel lift and/or strain on your Achilles' tendon.  However, if you do not have a limited range of motion, you can set it to whatever setting gives you more control/balance/feel.  But to change this for what terrain you are on is a little misleading, since at the very least you will be changing your body's balance point each time you switch it up.