Specifying dot gain curves for custom CMYK profile

Question

I am trying to create a custom CMYK profile that would mimic the FOGRA39 (coated) ICC profile but would provide more control.
When creating a custom ICC profile, I'm trying to specify the dot gain curves manually by entering the Tonal Value Increase data published by the International Color Consortium. But the last data point at far right (100 on the horizontal axis) always remains at 100% high instead of the appropriate 0%. In other words, the point at the top right corner should actually be at the bottom right corner. The point is uneditable, because it doesn't have a corresponding 100: entry field.
This is how the curve should actually look like:
I want to place the last point at the bottom right corner but I cannot figure out how to do that. I'm using Photoshop CC 2014 on Windows 8.1.
Do I misunderstand anything about the dot gain curves? Is this a bug? Does it actually affect the dot gain for dark shadows or is it merely a display problem?
I would appreciate any pointers to information about this problem.

Answer 1

Thank you. I have figured out by experimentation that you are right. I've fixed my dot gain curves to look like this: