Hope it helps. If I remember correctly, those are just concepts as it relates to other marks. Don't be afraid to tweak them to suit the terrain, wind, cover, etc. You want to put marks where the dog doesn't want to go or gets deflected off line from not fighting the factors.
But, there are times a flat field is useful too. Especially for ABC type drills where you teach gun relationships. Don't get so caught up in throwing difficult marks (and multiples) that the dog is always failing. It's all about balance.
Yes, we throw lots of difficult singles, to teach the dogs to handle the factors, but sometimes, we back off and let them have some therapy marks too.
Try to train with the most accomplished trainers/judges you can. You'll learn a lot from asking questions about how they formulate the sets. I'm very lucky that everyone in my group is a well-seasoned judge, most of us are both field trial and hunt test judges. So...we sit and analyze every set, discussing it before we reach a consensus. The emphasis is to train hard, test easy.
A really good group can be hard to break into because they're so insular. You have to earn your dues by throwing birds, being dedicated and working hard.