Hi Dan.C, sorry for the late reply, hope I'll be able to help you out anyway.
You are correct in that the elevated K block is the closest to the stage.
If you have a K ticket, you will have the chance to be really close to Ayu at 1 or 2 points during the concert, when she runs to the edges of the stage (you can see this in the DVDs). However, you're watching the concert from a 170-180degree angle, which makes you miss out on most of the light show. In addition to that, K tickets are ridiculously expensive, on par with decent A block tickets.
A C block ticket will be way cheaper, you'll see the concert head on and if you're in the middle of the C block you'll be pretty close to Ayu when she runs out to the central stage, if there is one. Try to get 1-3 row tickets in one of the middle C blocks.
D block tickets are very far from the stage, you'll still see the light show and everything, but Ayu will be tiny.
In my opinion, the best tickets possible to buy would be in the middle of the B block, as close to the center stage as possible. You'll see the concert from the angle it's mean to be seen and you'll also get scarily close to Ayu
.