Summon skeletons numbers

I was updating my char on PoB and noticed the difference between lvl 19 and lvl 20 is massive. At lvl 19 the average damage of a lightning projectile is 3,692. At lvl 20 it jumps to 9,539. At lvl 21 it jumps to 10,574.

Why is there such a big jump from 19 to 20? I checked the leveling damage on wiki and got the following:

68 1722 0.93 512–1280 (lvl 19)
70 1897 0.93 565–1412 (lvl 20)
72 2090 0.93 624–1560 (lvl 21)

The damage difference (far right column) should actually be more for 20 -> 21 then 19 -> 20. Additionally the cast speed remains the same (.93) so I'm wondering what I'm not seeing? Thanks in advance!

19-20 is a much bigger jump required in exp than previous levels

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seanxjohnson wrote:

At lvl 19 the average damage of a lightning projectile is 3,692. At lvl 20 it jumps to 9,539. At lvl 21 it jumps to 10,574.

the skeleton mage chart is most likely bugged in PoB