Difficulty interpreting PRISM Drugs AUC values

Greetings everyone,
I am trying to identify drugs that are sensitive against a specific group of cancer cell lines with specific features, and then do like a differential analysis to see if they are also statistically significant compared to control group of cell lines.

Anyways, I figured out the best way to do so is the AUC values since they measure the cumulative effect of the drug against multiple concentrations, and I assume the values are normalized. My problem is that I do not know how to interpret the AUC values.

Well, we know that the fitted graph in the first place measures the logarithmic fold change of cells compared to DMSO treated controls against drug sensitivity. That would essentially mean for drugs in negative correlation, a smaller AUC will indicate a more effective drug as u can imagine the the number of cells is further decreasing with the concentration making the area under the curve even smaller.

The problem arises if the drug is really effective since the start, so it has a negative log fold change, and that keeps further decreasing across the concentrations. In that case, since all the portion of the graph is decreasing under the 0 of the y-axis, a higher AUC would meaning the drug is more effective drug.

How can I deal with this? Did I misunderstood something?Thanks!