Would "Increased area of effect" passive work with "melee splash" support gem?

???

Yes

http://pathofexile.gamepedia.com/Melee_Splash

Keywords: Support, Melee, Attack, AoE

Stat modifiers from any source which would apply to an AoE skill will also apply to the AoE component of Melee Splash. These mods include:
- Area of Effect radius
- Area Damage

So, as KG31459, yes.

Yes. Conc effect works too (both reducing the AoE and multiplying the damage), although the damage multiplier is not obvious from the skill tooltip.

Concentrated effect would actually work for the AoE part only so the the monster you initially hit won't get CE damage bonus.

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gathor wrote:

Concentrated effect would actually work for the AoE part only so the the monster you initially hit won't get CE damage bonus.

Yes, that's why it's not apparent from the tooltip. Melee Splash is a bit confusing in this regard - it seems that you can actually do more damage to other monsters than you do to the initial target.

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Incompetent wrote:

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gathor wrote:

Concentrated effect would actually work for the AoE part only so the the monster you initially hit won't get CE damage bonus.

Yes, that's why it's not apparent from the tooltip. Melee Splash is a bit confusing in this regard - it seems that you can actually do more damage to other monsters than you do to the initial target.

With conc effect - most certainly.
Fixed the wiki page a bit, maybe that one will get asked a bit less now.

To provide numbers:

melee splash lvl 20: 28% less damage to other targets
conc effect lvl 20: 69% more area damage

combined: (1-0,28) * (1+0,69) = 1,21

Main target melee splash modifier: 16% less damage = 0,84

So you are actually doing 45% more damage to surrounding targets... Funny.