Dual zone conicals

Can anyone explain how dual zone conicals work?

There are two jackets that can cool the beer. Usually there is a jacket around the cone and a jacket for the rest of the cylinder. The jackets are filled with refrigerated glycol.

If I remember correctly it's because the yeast accumulating in the cone can be at a higher temperature.

So does this mean you have two thermowells, one at the cone and one on the sidewall that can feed two separate PIDs which in turn control two different valves so you have full independent zone control? Or do you have one pid controlling one valve and the zones are more for balancing glycol flow?

Brewers Hardware responded to me on this question with great detail. It was much appreciated by me and I will sum it up here in case others want to know.

They say the purpose is to promote convection currents. Ideally a ferment is temp controlled by the sidewalk jackets alone. This allows the colder upper level to fall towards the cone creating the current effect. If the cone jacket is used simultaneously the convection effect is lost. The conical jacket would be used for cold crashing or getting down to pitching temp. So in a proper setup, while there is only one thermowell in smaller systems, two separately controlled lines would need to feed the conicals jackets.

Brewers Hardware stated they feel the convection effect is going to maximize in larger conicals, stating the 30 gallon to 1 barrel size they offer to be better suited for the effect.