2.10.3.6 (1/28/24) dev_2, correct?
There is no user adjustment for the red line. Warren, Richie and I proved that it is mathematically correct, regardless of how it may look to some. IMHO it is spot on. Indeed, Richie's algorithm for calculating it is incredibly elegant, working for nearly any set of band conditions from empty to crowded. And it is very complete mathematically, accounting for FFT bin size and a host of other factors. It's so good that at my urging Richie added the noise power spectral density (NPSD) and passband noise power (PBNP) measurements to the info line.
Even if you don't agree that it is correct it's still irrelevant. If you are not happy with where the green line is landing simply change the offset and time constant values as desired:

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Remember that it only works with the spectral display in panafall mode.