I just read your post after (slowly, painfully slowly
) typing out the last response.
You can't argue with success -- if it works properly in both heating and cooling modes, then pat yourself on the back & leave your wallet in your pocket!
By rotating the temperature wheel on the shaft you are rebalancing the resistance chain comprised of the two thermistors & the potentiometer. As you may already know, the amplifier reads this resistance and supplies voltage to drive the servo until another potentiometer within the servo matches the resistance; this is how the servo ‘ knows’ where to stop within its internal travel. By adjusting the wheel, you may be making up for deficiencies elsewhere -- but like I said if it works, W. T. H.!