If you look at some of the earlier Corvette LT1 tunes PE/COT Spark Advance Correction (ECM 12634) the earlier (2015) LT1 tunes have to reduce timing at higher EQ ratios (richer). If you look at a 2016 Corvette LT1 tune it has the opposite, increases timing at higher EQ (richer) ratios and decreases at lower EQ ratios (leaner). Now I doubt the Corvette or Camaro development team was involved in the calibration but I would assume it was probably a global powertrain team and they maybe consulted the design team a few times but it was probably there decision? I have also heard the calibrations aren't even made by a human and are somehow automatically (AI? I don't believe there is a such thing as AI) populated based on data collected from engine dynos and the lab. Although I really really doubt GM would let a calibration go to production without letting at least one human look it over and make sure it looks somewhat ok.
Anyway it seems the entire internet and everyone else can't come to a definitive conclusion on spark advances dependence on AFR or if it is even dependent at all? As with everything else I'm sure it just depends and there is no generalization you can follow.
Its also possible that maybe when the table got programmed into HP Tuners someone missed that it was supposed to be in Lambda instead of EQ which would explain why they are opposite each other.