Concentration (armor Powder Special)

Can anyone tell me how the duration for concentration works? Does it just continuously add on more time as you use more and more mana? So if I were to use a spell that costs 6 mana, it would have a duration of 6 secs. But if I were to let the timer drop to 2 secs and then use another spell that costs 6 mana, would it increase to 8 secs?

Also as a side question, does having multiple armor pieces with concentration (or any other special) make the effect stack?

 

I've been told this and have not tested it myself. I was told this around the time Corkus came out, so something might have changed/will change in 1.19.

If you were to use a spell that costs 6 mana and let the timer drop down to 2 after four seconds after which you use this spell again, it'd reset to 6 mana.
multiple armor pieces with concentration do make the effect stack.

as a side note: keep in mind that concentration only boosts water damage.