The important thing to understand about the different decarboxylation graphs like this one, is how the experiment was performed. In this one note that it was marijuana extract placed on a hot glass surface in an open reactor. You don't get the same results decarboxylating using other processes like herb in the oven.
The above curve shows the peak THC achieved at about 70% of total THC-A, because at that point the THC-A is depleted and the same heat that is converting THC-A into THC, is breaking down the existing THC into its lower states like CBN. It is also breaking down the CBN, so that it doesn't rise in the same proportions.
The easiest way that I've found is to precisely decarboxylate the concentrate is after extraction so that I can watch the CO2 bubble formation. You will note from the link that I previously posted that Ghee or Clarified butter's smoke point is 252C/485F, which means that after you have filtered the plant material out, you can heat it to 121C/250F in a hot vegetable oil bath and watch the bubbles.
You have hit the peak of the above extraction curve when bubble production suddenly drops off at 70%, which is the maximum THC stage, but if you wish a more sedative med, continue to heat until bubble free.
Here's a link to some more decarboxylation data:
10.1.4 Decarboxylation 101 - GrayWolf's Lair