I'm not 100% sure I'm interpreting your comment correctly, but higher orbits will always decay more slowly, all other things being equal. There's just far less

I'm not 100% sure I'm interpreting your comment correctly, but higher orbits will always decay more slowly, all other things being equal. There's just far less atmosphere to bleed off the energy. Edit: I think I now understand what you mean, but I suspect you're not realizing that every satellite appears twice on the chart: once in blue, for its periapsis (perigee, i.e. low point of its orbit), and once in red, for its apoapsis (apogee, i.e. high point of its orbit). You're probably noticing that some of the red dots, at high altitude, are decaying quickly, but that's because the corresponding blue dots are at low altitude. Note also that orbital period is a monotonic function of altitude. More precisely, the square of orbital period goes with the cube of the semi-major axis (the long axis of the orbital ellipse).