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As I understand, the fine tuning for KU is a bit trickier than for C-band.
The LNB has to be accurately centered, pointed to the middle of the dish, and adjusted for focus, as well as the usual dish alignment.
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I agree that it is very important to have the feed at the proper focal point. Relative to being centered, again I agree, because there is only one focal point of a dish, so it's important that the feed be at the focal point.
However, while it's ideal to have the feedhorn aimed at the center of the dish, I'm not convinced that it makes a whole lot of difference.
My nearest true south satellite has been AMC6, and I have used it for alignment. But unfortunately a couple pine trees had grown up and partially blocked my view of AMC6, and I hadn't realized that this was happening. Basically, the pine tree was blocking the bottom half of my dish.
Anyway, I noticed something interesting while trying to align my dish. I was up on a high perch (the bucket of the front end loader of my tractor) trying to adjust the focal length of my feed while aimed at AMC6, and I noticed that if I twisted the feed so that it was NOT aimed at the center of the dish, but instead aimed about half way from the center to the upper edge, that my signal was significantly greater. This had me REALLY confused for a while, until I looked at where the dish was aimed, and noticed that the pine tree was blocking the view, and this was later confirmed during a solar outage period, when the whole bottom half of the dish was shaded. Basically, with a BUD, despite the scalar rings, the feeds are much better at illuminating the center 3 or 4' diameter of the dish, and gets very little from out at the edges, but if the center and bottom half of the signal is blocked, and most of the signal is coming from the top, you are better off twisting the feed to aim at the portion of the dish that is actually reflecting signal. This is essentially what an offset dish feed does, ie it doesn't aim at the center of the paraboloid (elipsoid), but aims at where the reflection is coming from.
Anyway, after learning that, I have since adjusted my focal length, feed aim when looking at sats I have a good unblocked view of, and then, I got maximum signal aime near the center, however there wasn't really all that much improvement when I'd twist the feed to aim at different parts of the dish. So yes, it's best to be aimed at the center of the dish, but I really don't think it's that critical, and I think that it's overkill to go to the lengths that some people go to, such as using lasers, and other things to insure that the feed is aiming EXACTLY at the center. It's just not that important.
But being at the focal point IS important. Assuming that your dish actually has one.
( I've hit my dish with a broom so many times that I'm not sure that it has a focal point anymore.)
