Steve, I see exactly that the problem is a cumulative error. Because the image is one pixel higher than it should be before I start the imaging process, when I slice the image, the pixels that are closest to the center are fine. As you move farther from then center, the error becomes noticeable and if you've used an extreme angle, you are a lot further from the center so the error continues to grow. When I repeat this process for the second generation, that image is now two pixels too high and the slicing and rotation of that image makes the discrepancy more noticeable. But moving the image down by one pixel will simply make the same error on the bottom of the image. Making a change that will fix this means changing code in lots of places which is why it will not be a simple fix.
As you accurately pointed out, the center of the design is as perfect as it needs to be even if you use extreme angles. So I appreciate that you pointed this out to me because I never noticed it in the past 12 years. I never noticed it because I would ever make a design with an extreme angle because in practice, the same slicing/rotation would make it hard to maintain quality.
Because of this, this issue has a ways to go before it gets to my top priorities list.