Can someone explain AMBROSIA gem?

I have 120 max charges in Ultimate mana flask. But unfortunately i don't see any difference in skills dps.

With 120 max charges in mana flask i should have seen 3% × 24 = 72% extra lighting damage.

It is bugged or what I'm missing???
Maybe it needs to use mana flask before to trigger the effect? I don't know.

Curious about this as well, got a flask with 70% increased charges and seems a waste...

You don't see a change in ingame dps when you remove the gem, but you notice the dmg increase if you have no flask charges.

I don't understand the use of this gem. Seems to me doesn't work.

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bobsponge123#5749 wrote:

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It actually works really well, I have cold monk with Call of the Brotherhood ring (converts all lightning to cold) and thanks to this gem on my tempest bell Im shocking bosses.

Since only way how to deal lightning damage in this case is a source of "gain X% damage as extra" (it happens after the conversion) and this gem is the only source of this on my build.