Actually, I am pretty sure the TS is not the average of all the science scores. They add up how many questions you got wrong in the Bio, orgo, chem and physics and subtract it out of 140 (100 in Science and 40 in Physics) and then scale your score based on that number. There have been times where none of the individual science section scores are as high as the TS score. Thats why it works in your favor.
AA is the average of your individual scores on each section.