/6 torsion bars

It's the stored energy in the loaded bar.

Think of it like this. If you have a 50lb spring and a 100lb spring, same static height, if you compress the 50lb spring to get it to 100lb like the static natural state of the 100lb spring, which one will spring more when released.

Same deal with a /6 bar vs 318 or 340 bars. The rate on the /6 bars is less, so to get them to hold a front end up at same height requires more preload than a bigger bar. The /6 bars have more stored energy at ride height. The bars you want are /6, no AC bars.