Arcane surge Force of Will scales on different mana pool, intended or bug?

If we look at the description of Force of Will, it states:
"1% increased Effect of Arcane Surge on you per 15 maximum Mana."

Naturally, we would assume that "maximum Mana" refers to the total maximum Mana we see on our screen.

For example, let’s say we have 7,653 Mana. We know this is our maximum Mana because it is displayed in the UI, we can use it until it depletes, and it also works for effects like taking hits through Mind over Matter (MoM).

However, the Force of Will notable doesn't calculate its increased effect based on this visible Mana value. Instead, it uses the "maximum Mana" value shown in the passive tree tooltip. You can check this by holding Shift and hovering over any passive node that affects Mana. And what do we see there? It shows 5,568 Mana.

This is confusing because the Mana displayed in the passive tree tooltip is lower than the maximum Mana we see on our screen. Why is that? Shouldn't our maximum Mana be 7,653, as shown in the UI? This discrepancy leads to the issue we’re facing.

The Problem with Gear and Weapon Swaps
This issue becomes more apparent when we start swapping gear.

Let’s take a weapon with the following modifiers:
+145 to Maximum Mana
+33 to Intelligence

As expected, equipping this weapon increases our maximum Mana. The visible Mana in the UI goes up. But wait—why hasn’t my cast speed changed? After all, I increased my maximum Mana, and the Force of Will notable literally says it scales with maximum Mana. Something feels off.

When I remove the weapon, my maximum Mana drops back to the previous number, as expected. But again, there’s no change in cast speed. Why is this happening?

The same thing occurs when I equip a shield. For example, I use Mahuxotl’s Machination Omen Crest Shield, which provides significant Mana through its 3 Mana Soul Cores. Equipping it grants me around +1,700 maximum Mana, which is a substantial increase. Yet, once again, my cast speed doesn’t increase. This inconsistency makes me question what’s really going on.

The Core Issue
The problem lies in how Force of Will calculates "maximum Mana." It doesn't use the total Mana shown on your screen (which includes bonuses from gear, buffs, and temporary effects). Instead, it calculates its effect based solely on the Passive Tree Maximum Mana, as displayed in the passive tree tooltip.

This means that bonuses from gear (like the weapon or shield mentioned earlier) are excluded from the calculation, even though they visibly increase your total Mana. As a result, equipping or unequipping gear has no impact on effects like cast speed that are tied to the Force of Will notable.

Arcane surge topic we discussed: https://github.com/PathOfBuildingCommunity/PathOfBuilding-PoE2/issues/258

Hi. I just started messing around with Path of Building 2 for my character and noticed my cast speed and mana regen was higher than in the game. I've been trying to reverse engineer why for the past hour or so. I ended up believing something with arcane surge effect was scaling differently and I was lacking like 70% arcane surge effect. But it wasn't as simple as Touch the Arcane wheel not working alongside Stormweaver ascendancy... they still stacked in the game tooltip.

Then I found this thread!

I am 99% sure this is because your weapon and off-hand not being counted by the passive tree. I suppose this has something to do with the weapon swap passive system. All my gear stats do scale arcane surge effect, except weapon and off-hand.

See in-game screenshot of my passive tree value and the mana value in PoB2 without a weapon or off-hand equipped.





Edit: This also seems to affect anything on the passive tree related to stats on your weapon and off-hand. Because many people report issues with Arcane Intensity as well.