Oooh, it's been a long time since I've been able to post my "Zena tutorial"!
Yes, the Zena should be tightened from the bottom up. Steps are as follows: 1) Loosen ALL the straps; 2) pull the Zena down from the front bottom sides of the main part, not the front panels; 3) Tighten the lower straps completely (should sit at the hips); 4) Tighten the middle straps so they sit at the waist and under the ribs; 5) snug up the shoulder straps, there's no need to "tighten" them.
As far as I'm concerned this process is best done underwater when you're horizontal since that's your diving position. I find it impossible to get the right adjustment on land (or boat) with a tank on in a vertical position (sitting or standing).
So on land what I do is pull it down as much as I can, adjust from the bottom up, but if I'm shore diving I'll tighten my shoulder straps ALL the way down as it makes the tank for stable for me, if I'm boat diving, I tighten them about 1/2 way down (a bit more than their final adjustment) so I can get my tank stable.
Once in the water, I go horizontal during my descent, loosen all the straps and set my Zena in place. Takes all of about 10 seconds at the most. Once the Zena is properly positioned and adjusted, there should be ZERO tank roll or BC movement. The Zena should literally fit like a corset, which are very fitted to the body, snug but not tight.
I'd recommend strongly that you consider purchasing the new Zena lumbar pad and add-on pocket that Scott debuted earlier this year. The pocket is great because it goes on and off easily and can be used only when you need it (I use it for night diving mostly), and the lumbar pad fills the lower back space beautifully and for me makes my tank a bit more comfortable.
Hope this is helpful!
