On that area you will see movement early enough and make your decisions about casting etc. On that you don't have to move your head that you scan well. It doesn't mean that wouldn't be able cast other areas and scan them. You just will be slower and if not trained with casting and accuracy, you won't hit that easily. Straight behind of that angle is similar area where you can be accurate, just how to observe that, that is million dollar question.
When you see rise or something that you need put your mind on, do not stare one point, keep your eyes run to left and right, otherwise they will tire and you will lose accuracy. And now comes important part, when you run your eyes, do it on same distance what you are observing. The idea is that your eyes has been adjusted for certain distance, like binoculars, and they don't have to work more with adjusting.
One more tip is about for which direction you scan. Paul pointed that out and it was funny that, it is exactly what I do all the time. When I'm driving snowmobile I like to watch on the left, which means that all the tracks and footprints are coming from right to left. Sometimes I try to do other side but I have to slow down a lot to see everything clearly. Paul told that it is based on reading, we normally read from left to right and we skip words because we kind of can guess some of the words. If you read same line from right to left you need read every word to make sense. So scan water starting from right to left and then back. You will be more concentrated and see more small details.
So do not just improve your casting and accuracy, do it also how you scan water. It can make that small difference to catch a fish.
Have a nice weekend and go fishing
Mika the Legend
Ps. This has been written over Malaysia when flying back home