No the cattle don't read the "rules" that is why as a rider you need to set yourself up to be able to see and anticipate what those cattle are going to do. I too have stopped cattle in the hole successfully with my horse sideways. I admit, though, that I ride horses that considered to be top cow horses. I also have over 30 years of working cattle on horseback under my belt. I assume that you are similar in experience and horse power to myself.
But the OP is a beginner and I am assuming the horse is also new to sorting. Based on that and also on everything that I have been taught from some top clinicians, I do advocate the "do not ever" let your horse go sideways in the hole. By doing so your horse's eyes are no longer on the cattle, decreasing your chances of stopping trash. As well when the horse is sideways it requires more time to swing back into position to make a move on cattle over a quick move to the left or right or even towards the cattle coming at them. By using the hip to stop trash, it can cause your horse to become even further out of position increasing the chances of another animal slipping past you and your horse.
I have also learned both from clinics and experience, tunnel vision when playing any position can cost your team a run. Even when you are pulling you need to be aware of the rest of the herd and where they are going, not just the cow that you are trying to pull.
You are correct mls, communication is the key to a successful run.