nobody has followed up on this, thanks for checking.
what about instead of increasing/decreasing the chain length by 50% you try setting it to what the chain length should be for the position actually cut (or 90% of the difference between what it thought it was and what it ould have been for that cut)
One interesting thing about the calculations being done in radians, it actually forms triangles and you can calculate where the top of the triangle would be if the chain wrapped around the sprocket were to be straight (if you dig into the math enough to make your head spin, you will see that it’s doing exactly that in the normal kinematics)
by the way, your testing is complicated by the fact that the chain lengths are incorrect, see What is correct chain pitch? and Whats inside the gearbox/motor? so that you can change the encodersteps variable and eliminate a 0.4% error that you didn’t know you had.