Triple post, sorry.
I did a little experiment with spirit/no spirit and sitting/standing to see how it affected my mana and health regen.
First picture. Here I'm standing with base spirit (60) and my regen is 14 health and 27 mana per tick.
Second picture. Here I'm sitting with base spirit (60) and my regen is 18 health and 27 mana per tick.
As you can see, sitting does not have any effect on your mana regen.
Third picture. Here I'm standing with spirit bonus on (93 total spirit) and my regen is 17 health and 34 mana per tick.
Fourth picture. Here I'm sitting with spirit bonus on (93 total spirit) and my regen is 22 health. Unfortunately my mana pool was regenerated before I managed to hit the screenshot button, but the mana regen was still 34 per tick.
As you can see from comparing those four pictures, sitting down gave me about +5 to my health regen. More spirit increased my base regen, but it did not increase the +5 health regen.
Hopefully this cleared up some thing. I sure hope those links work.