for example
Point A is a min bet.
Point ? is undefined without stack information; Point ? may very well be all in somewhere far above the 0ev line with a strong hand.
The curve is the bettor's ev, which is a function of potsize.
It could very well be that the curve starts above the 0ev line on the left and ends below the 0ev line at point ?, as would happen with a thin value hand.
I just drew it the way I did for simplicity.