Arcmage Reservation Efficiency Miscalculation

The Arcmage spirit gem, at max quality, says it has 10% increased reservation efficiency. The base gem takes 100 spirit. A 10% reservation efficiency should mean it then takes 90 spirit, but it instead takes 91 spirit. I expect this is some kind of floating point rounding / ceiling issue.

I know it's just one spirit, but this is the difference between being able to run Clarity I with the skill and no spirit on my gear and needing to allocate spirit on my gear.

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seaman#4993 wrote:

100 / (1 + 0.1) = 90.9 ≈ 91
https://www.poe2wiki.net/wiki/Reservation#Reservation_efficiency

I see, how annoying - okay thank you.