How did you measure this? I have to admit, I basically 'estimated' the results on my end and adjusted the displayed values in the GUI to match the intended behavior pretty closely. But, definitely not as precise as you did here.
Still relying on internal_level = threshold_in_%*gain_reduction^(ratio/(1 - ratio)) with gain_reduction = output/input.
No clue what you mean by adjusted GUI: The GUI shows gain reduction. The speed of a 86% gain reduction depends on the threshold, so one could only get it right for one specific case, e.g. setting threshold = -36dB and play a sine wave and adjust the GUI to match. However no other threshold will have correct attack timings then.
Release seems to work exactly the same as attack just in the opposite direction what I consider a good and useful thing. Not even able to think about a way to have it defined by going up 10dB per release time (in ST I mean).
NOTE: I'm using shapes = 500 here all the time. So maybe the situation differs from shapes = 1.
The change at 100 ms is weird. Does it maybe depend on the frequency of the tone that you play? If I'm guessing correctly, moving the frequency to 500 Hz would move this point to 200 ms...
No, I tried 100Hz, 500Hz and 10kHz, all the same. But I don't know if this is a problem at all.
No need to change anything. Even though I guess my measurements are quite accurate I'm unsure if I measure the right thing i.e. use your intended definition.