Yes, it’s inverse. The stronger you are the shorter a high you enjoy before you get the comedown. But it wouldn’t last forever with 1 strength, no.
To give you a more detailed answer as to why it’s only affecting meth: Adderall and cocaine grant their benefits by giving you a stimulant effect. This is straightforward. Meth does this as well, but also has its own set of more complex effects that are separate - first high on meth, then meth comedown. The idea is that it gives you a drastic short term effect, and then a long term penalty. The equation that it uses just doesn’t account for strength values as high as you’ve set yours.