Anyone know how the mana regen ticks work?

[Crenshinabon]

So I am playing a shaman.
Have to stand frequently to canni.

I have tried to judge when best time to cast is, so I try to cast in between ticks. Thing is sometimes the tick happens when it should but sometimes it seems like it doesnt. On top of that sometimes if I stand after the tick it goes back down. On top of that sometimes it ticks twice.



Whats the deal? Does it even matter when I stand or am I literally losing out on mana by not sitting at the correct times? And if thats the case why does the tick sometimes go away and why sometimes tick twice?

Thanks!
=P